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 $204.60   13.197%   $231.6011   $231.60   $231.60   $231.60  
  Purchase #2 $180.53   7.833%   $194.6709   $194.67   $194.65   $194.70  
  Purchase #3 $26.80   5.580%   $28.2954   $28.30   $28.30   $28.30  
  Purchase #4 $155.37   4.744%   $162.7408   $162.74   $162.75   $162.70  
  Purchase #5 $53.55   12.345%   $60.1607   $60.16   $60.15   $60.20  
  Purchase #6 $125.43   7.584%   $134.9426   $134.94   $134.95   $134.90  
  Purchase #7 $228.73   7.219%   $245.242   $245.24   $245.25   $245.20  
  7 purchase totals = $975.01       $1,057.6535   $1,057.65   $1,057.65   $1,057.60