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 $196.39   11.241%   $218.4662   $218.47   $218.45   $218.50  
  Purchase #2 $135.67   9.697%   $148.8259   $148.83   $148.85   $148.80  
  Purchase #3 $33.91   10.569%   $37.4939   $37.49   $37.50   $37.50  
  Purchase #4 $97.32   5.727%   $102.8935   $102.89   $102.90   $102.90  
  Purchase #5 $84.28   10.114%   $92.8041   $92.80   $92.80   $92.80  
  Purchase #6 $219.88   8.159%   $237.82   $237.82   $237.80   $237.80  
  Purchase #7 $126.57   4.791%   $132.634   $132.63   $132.65   $132.60  
  7 purchase totals = $894.02       $970.9376   $970.93   $970.95   $970.90