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 $91.55   10.314%   $100.9925   $100.99   $101.00   $101.00  
  Purchase #2 $49.99   7.279%   $53.6288   $53.63   $53.65   $53.60  
  Purchase #3 $58.95   7.119%   $63.1467   $63.15   $63.15   $63.10  
  Purchase #4 $5.61   11.603%   $6.2609   $6.26   $6.25   $6.30  
  Purchase #5 $54.95   7.265%   $58.9421   $58.94   $58.95   $58.90  
  Purchase #6 $167.51   11.185%   $186.246   $186.25   $186.25   $186.20  
  Purchase #7 $222.93   9.483%   $244.0705   $244.07   $244.05   $244.10  
  7 purchase totals = $651.49       $713.2875   $713.29   $713.30   $713.20