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 $231.65   10.524%   $256.0288   $256.03   $256.05   $256.00  
  Purchase #2 $102.54   7.571%   $110.3033   $110.30   $110.30   $110.30  
  Purchase #3 $120.82   10.679%   $133.7224   $133.72   $133.70   $133.70  
  Purchase #4 $153.78   13.702%   $174.8509   $174.85   $174.85   $174.90  
  Purchase #5 $82.68   10.822%   $91.6276   $91.63   $91.65   $91.60  
  Purchase #6 $25.81   4.113%   $26.8716   $26.87   $26.85   $26.90  
  Purchase #7 $158.58   3.561%   $164.227   $164.23   $164.25   $164.20  
  7 purchase totals = $875.86       $957.6316   $957.63   $957.65   $957.60