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 $207.91   13.299%   $235.56   $235.56   $235.55   $235.60  
  Purchase #2 $89.29   6.270%   $94.8885   $94.89   $94.90   $94.90  
  Purchase #3 $45.63   12.121%   $51.1608   $51.16   $51.15   $51.20  
  Purchase #4 $103.61   3.787%   $107.5337   $107.53   $107.55   $107.50  
  Purchase #5 $119.43   12.505%   $134.3647   $134.36   $134.35   $134.40  
  Purchase #6 $97.73   13.740%   $111.1581   $111.16   $111.15   $111.20  
  Purchase #7 $230.66   9.851%   $253.3823   $253.38   $253.40   $253.40  
  7 purchase totals = $894.26       $988.0481   $988.04   $988.05   $988.20