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 $212.37   11.381%   $236.5398   $236.54   $236.55   $236.50  
  Purchase #2 $94.32   12.353%   $105.9713   $105.97   $105.95   $106.00  
  Purchase #3 $206.87   9.366%   $226.2454   $226.25   $226.25   $226.20  
  Purchase #4 $224.71   9.644%   $246.381   $246.38   $246.40   $246.40  
  Purchase #5 $32.41   11.151%   $36.024   $36.02   $36.00   $36.00  
  Purchase #6 $160.69   9.260%   $175.5699   $175.57   $175.55   $175.60  
  Purchase #7 $191.97   9.759%   $210.7044   $210.70   $210.70   $210.70  
  7 purchase totals = $1,123.34       $1,237.4358   $1,237.43   $1,237.40   $1,237.40