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 $223.83   13.347%   $253.7046   $253.70   $253.70   $253.70  
  Purchase #2 $117.86   12.451%   $132.5347   $132.53   $132.55   $132.50  
  Purchase #3 $5.25   7.107%   $5.6231   $5.62   $5.60   $5.60  
  Purchase #4 $148.26   10.442%   $163.7413   $163.74   $163.75   $163.70  
  Purchase #5 $241.36   10.589%   $266.9176   $266.92   $266.90   $266.90  
  Purchase #6 $240.75   5.675%   $254.4126   $254.41   $254.40   $254.40  
  Purchase #7 $22.42   6.311%   $23.8349   $23.83   $23.85   $23.80  
  7 purchase totals = $999.73       $1,100.7688   $1,100.75   $1,100.75   $1,100.60