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 $146.97   11.791%   $164.2992   $164.30   $164.30   $164.30  
  Purchase #2 $50.76   5.317%   $53.4589   $53.46   $53.45   $53.50  
  Purchase #3 $19.48   12.649%   $21.944   $21.94   $21.95   $21.90  
  Purchase #4 $74.79   12.591%   $84.2068   $84.21   $84.20   $84.20  
  Purchase #5 $193.36   8.617%   $210.0218   $210.02   $210.00   $210.00  
  Purchase #6 $226.42   4.185%   $235.8957   $235.90   $235.90   $235.90  
  Purchase #7 $210.34   6.716%   $224.4664   $224.47   $224.45   $224.50  
  7 purchase totals = $922.12       $994.2928   $994.30   $994.25   $994.30