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 $194.46   5.283%   $204.7333   $204.73   $204.75   $204.70  
  Purchase #2 $239.77   11.541%   $267.4419   $267.44   $267.45   $267.40  
  Purchase #3 $25.31   13.419%   $28.7063   $28.71   $28.70   $28.70  
  Purchase #4 $89.45   13.143%   $101.2064   $101.21   $101.20   $101.20  
  Purchase #5 $178.60   3.481%   $184.8171   $184.82   $184.80   $184.80  
  Purchase #6 $187.62   9.383%   $205.2244   $205.22   $205.20   $205.20  
  Purchase #7 $172.79   13.797%   $196.6298   $196.63   $196.65   $196.60  
  7 purchase totals = $1,088.00       $1,188.7592   $1,188.76   $1,188.75   $1,188.60