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 $165.49   8.366%   $179.3349   $179.33   $179.35   $179.30  
  Purchase #2 $157.87   6.631%   $168.3384   $168.34   $168.35   $168.30  
  Purchase #3 $182.30   6.864%   $194.8131   $194.81   $194.80   $194.80  
  Purchase #4 $152.28   7.815%   $164.1807   $164.18   $164.20   $164.20  
  Purchase #5 $84.50   3.350%   $87.3308   $87.33   $87.35   $87.30  
  Purchase #6 $60.62   11.192%   $67.4046   $67.40   $67.40   $67.40  
  Purchase #7 $193.46   12.671%   $217.9733   $217.97   $217.95   $218.00  
  7 purchase totals = $996.52       $1,079.3758   $1,079.36   $1,079.40   $1,079.30