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 $47.80   13.567%   $54.285   $54.29   $54.30   $54.30  
  Purchase #2 $241.92   4.568%   $252.9709   $252.97   $252.95   $253.00  
  Purchase #3 $47.74   4.654%   $49.9618   $49.96   $49.95   $50.00  
  Purchase #4 $220.93   10.539%   $244.2138   $244.21   $244.20   $244.20  
  Purchase #5 $162.87   6.214%   $172.9907   $172.99   $173.00   $173.00  
  Purchase #6 $8.46   10.516%   $9.3497   $9.35   $9.35   $9.30  
  Purchase #7 $43.99   11.183%   $48.9094   $48.91   $48.90   $48.90  
  7 purchase totals = $773.71       $832.6813   $832.68   $832.65   $832.70