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 $59.80   11.491%   $66.6716   $66.67   $66.65   $66.70  
  Purchase #2 $64.34   11.400%   $71.6748   $71.67   $71.65   $71.70  
  Purchase #3 $161.79   10.333%   $178.5078   $178.51   $178.50   $178.50  
  Purchase #4 $241.89   5.283%   $254.669   $254.67   $254.65   $254.70  
  Purchase #5 $207.81   6.218%   $220.7316   $220.73   $220.75   $220.70  
  Purchase #6 $161.90   9.113%   $176.6539   $176.65   $176.65   $176.70  
  Purchase #7 $24.39   10.746%   $27.0109   $27.01   $27.00   $27.00  
  7 purchase totals = $921.92       $995.9196   $995.91   $995.85   $996.00