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 $247.50   13.518%   $280.9571   $280.96   $280.95   $281.00  
  Purchase #2 $61.62   13.399%   $69.8765   $69.88   $69.90   $69.90  
  Purchase #3 $227.25   7.625%   $244.5778   $244.58   $244.60   $244.60  
  Purchase #4 $240.76   13.753%   $273.8717   $273.87   $273.85   $273.90  
  Purchase #5 $240.79   8.295%   $260.7635   $260.76   $260.75   $260.80  
  Purchase #6 $181.46   5.456%   $191.3605   $191.36   $191.35   $191.40  
  Purchase #7 $154.25   5.609%   $162.9019   $162.90   $162.90   $162.90  
  7 purchase totals = $1,353.63       $1,484.3090   $1,484.31   $1,484.30   $1,484.50