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 $86.66   11.688%   $96.7888   $96.79   $96.80   $96.80  
  Purchase #2 $41.54   11.575%   $46.3483   $46.35   $46.35   $46.30  
  Purchase #3 $196.63   8.321%   $212.9916   $212.99   $213.00   $213.00  
  Purchase #4 $197.37   9.231%   $215.5892   $215.59   $215.60   $215.60  
  Purchase #5 $41.45   11.579%   $46.2495   $46.25   $46.25   $46.20  
  Purchase #6 $19.59   3.338%   $20.2439   $20.24   $20.25   $20.20  
  Purchase #7 $204.28   12.756%   $230.338   $230.34   $230.35   $230.30  
  7 purchase totals = $787.52       $868.5493   $868.55   $868.60   $868.40