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 $68.27   9.426%   $74.7051   $74.71   $74.70   $74.70  
  Purchase #2 $216.60   9.837%   $237.9069   $237.91   $237.90   $237.90  
  Purchase #3 $17.96   13.227%   $20.3356   $20.34   $20.35   $20.30  
  Purchase #4 $188.96   9.707%   $207.3023   $207.30   $207.30   $207.30  
  Purchase #5 $46.72   3.872%   $48.529   $48.53   $48.55   $48.50  
  Purchase #6 $59.97   9.861%   $65.8836   $65.88   $65.90   $65.90  
  Purchase #7 $44.38   10.290%   $48.9467   $48.95   $48.95   $48.90  
  7 purchase totals = $642.86       $703.6092   $703.62   $703.65   $703.50