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 $28.83   13.591%   $32.7483   $32.75   $32.75   $32.70  
  Purchase #2 $85.71   9.435%   $93.7967   $93.80   $93.80   $93.80  
  Purchase #3 $107.80   11.573%   $120.2757   $120.28   $120.30   $120.30  
  Purchase #4 $199.71   3.340%   $206.3803   $206.38   $206.40   $206.40  
  Purchase #5 $8.67   4.858%   $9.0912   $9.09   $9.10   $9.10  
  Purchase #6 $238.30   11.277%   $265.1731   $265.17   $265.15   $265.20  
  Purchase #7 $161.95   8.377%   $175.5166   $175.52   $175.50   $175.50  
  7 purchase totals = $830.97       $902.9819   $902.99   $903.00   $903.00