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 $46.64   6.420%   $49.6343   $49.63   $49.65   $49.60  
  Purchase #2 $228.46   9.756%   $250.7486   $250.75   $250.75   $250.70  
  Purchase #3 $175.96   13.436%   $199.602   $199.60   $199.60   $199.60  
  Purchase #4 $26.73   8.258%   $28.9374   $28.94   $28.95   $28.90  
  Purchase #5 $205.32   8.736%   $223.2568   $223.26   $223.25   $223.30  
  Purchase #6 $150.77   9.319%   $164.8203   $164.82   $164.80   $164.80  
  Purchase #7 $54.61   3.215%   $56.3657   $56.37   $56.35   $56.40  
  7 purchase totals = $888.49       $973.3651   $973.37   $973.35   $973.30