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 $87.94   11.815%   $98.3301   $98.33   $98.35   $98.30  
  Purchase #2 $199.70   9.401%   $218.4738   $218.47   $218.45   $218.50  
  Purchase #3 $130.84   5.732%   $138.3397   $138.34   $138.35   $138.30  
  Purchase #4 $206.77   7.584%   $222.4514   $222.45   $222.45   $222.50  
  Purchase #5 $51.50   8.331%   $55.7905   $55.79   $55.80   $55.80  
  Purchase #6 $10.35   8.295%   $11.2085   $11.21   $11.20   $11.20  
  Purchase #7 $45.93   5.427%   $48.4226   $48.42   $48.40   $48.40  
  7 purchase totals = $733.03       $793.0166   $793.01   $793.00   $793.00