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 $29.51   13.595%   $33.5219   $33.52   $33.50   $33.50  
  Purchase #2 $96.58   11.460%   $107.6481   $107.65   $107.65   $107.60  
  Purchase #3 $158.96   9.265%   $173.6876   $173.69   $173.70   $173.70  
  Purchase #4 $78.53   5.671%   $82.9834   $82.98   $83.00   $83.00  
  Purchase #5 $197.63   13.536%   $224.3812   $224.38   $224.40   $224.40  
  Purchase #6 $68.76   6.224%   $73.0396   $73.04   $73.05   $73.00  
  Purchase #7 $68.58   10.554%   $75.8179   $75.82   $75.80   $75.80  
  7 purchase totals = $698.55       $771.0797   $771.08   $771.10   $771.00