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 $82.97   11.131%   $92.2054   $92.21   $92.20   $92.20  
  Purchase #2 $128.95   12.676%   $145.2957   $145.30   $145.30   $145.30  
  Purchase #3 $12.54   4.418%   $13.094   $13.09   $13.10   $13.10  
  Purchase #4 $88.55   12.554%   $99.6666   $99.67   $99.65   $99.70  
  Purchase #5 $244.72   3.348%   $252.9132   $252.91   $252.90   $252.90  
  Purchase #6 $157.79   13.130%   $178.5078   $178.51   $178.50   $178.50  
  Purchase #7 $67.31   9.842%   $73.9347   $73.93   $73.95   $73.90  
  7 purchase totals = $782.83       $855.6174   $855.62   $855.60   $855.60