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 $196.72   8.139%   $212.731   $212.73   $212.75   $212.70  
  Purchase #2 $43.42   12.641%   $48.9087   $48.91   $48.90   $48.90  
  Purchase #3 $150.81   9.206%   $164.6936   $164.69   $164.70   $164.70  
  Purchase #4 $215.42   3.158%   $222.223   $222.22   $222.20   $222.20  
  Purchase #5 $83.94   6.388%   $89.3021   $89.30   $89.30   $89.30  
  Purchase #6 $16.35   3.873%   $16.9832   $16.98   $17.00   $17.00  
  Purchase #7 $206.56   12.307%   $231.9813   $231.98   $232.00   $232.00  
  7 purchase totals = $913.22       $986.8229   $986.81   $986.85   $986.80