Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $235.70   13.586%   $267.7222   $267.72   $267.70   $267.70  
  Purchase #2 $117.58   12.772%   $132.5973   $132.60   $132.60   $132.60  
  Purchase #3 $96.91   10.190%   $106.7851   $106.79   $106.80   $106.80  
  Purchase #4 $165.26   10.648%   $182.8569   $182.86   $182.85   $182.90  
  Purchase #5 $241.67   13.687%   $274.7474   $274.75   $274.75   $274.70  
  Purchase #6 $216.46   12.450%   $243.4093   $243.41   $243.40   $243.40  
  Purchase #7 $134.39   8.435%   $145.7258   $145.73   $145.75   $145.70  
  7 purchase totals = $1,207.97       $1,353.8440   $1,353.86   $1,353.85   $1,353.80