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 $29.35   11.614%   $32.7587   $32.76   $32.75   $32.80  
  Purchase #2 $20.52   10.678%   $22.7111   $22.71   $22.70   $22.70  
  Purchase #3 $228.96   9.191%   $250.0037   $250.00   $250.00   $250.00  
  Purchase #4 $120.93   10.739%   $133.9167   $133.92   $133.90   $133.90  
  Purchase #5 $221.57   10.727%   $245.3378   $245.34   $245.35   $245.30  
  Purchase #6 $117.55   7.167%   $125.9748   $125.97   $125.95   $126.00  
  Purchase #7 $210.76   6.265%   $223.9641   $223.96   $223.95   $224.00  
  7 purchase totals = $949.64       $1,034.6669   $1,034.66   $1,034.60   $1,034.70