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 $59.59   11.332%   $66.3427   $66.34   $66.35   $66.30  
  Purchase #2 $194.63   12.401%   $218.7661   $218.77   $218.75   $218.80  
  Purchase #3 $95.72   13.646%   $108.782   $108.78   $108.80   $108.80  
  Purchase #4 $57.48   5.228%   $60.4851   $60.49   $60.50   $60.50  
  Purchase #5 $173.96   5.507%   $183.54   $183.54   $183.55   $183.50  
  Purchase #6 $170.89   10.637%   $189.0676   $189.07   $189.05   $189.10  
  Purchase #7 $167.40   8.681%   $181.932   $181.93   $181.95   $181.90  
  7 purchase totals = $919.67       $1,008.9155   $1,008.92   $1,008.95   $1,008.90