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 $172.48   13.642%   $196.0097   $196.01   $196.00   $196.00  
  Purchase #2 $210.69   11.226%   $234.3421   $234.34   $234.35   $234.30  
  Purchase #3 $11.37   9.234%   $12.4199   $12.42   $12.40   $12.40  
  Purchase #4 $25.47   9.139%   $27.7977   $27.80   $27.80   $27.80  
  Purchase #5 $204.54   11.282%   $227.6162   $227.62   $227.60   $227.60  
  Purchase #6 $235.99   3.479%   $244.2001   $244.20   $244.20   $244.20  
  Purchase #7 $91.35   8.245%   $98.8818   $98.88   $98.90   $98.90  
  7 purchase totals = $951.89       $1,041.2675   $1,041.27   $1,041.25   $1,041.20