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 $149.44   9.582%   $163.7593   $163.76   $163.75   $163.80  
  Purchase #2 $217.57   12.126%   $243.9525   $243.95   $243.95   $244.00  
  Purchase #3 $230.40   11.373%   $256.6034   $256.60   $256.60   $256.60  
  Purchase #4 $92.31   10.417%   $101.9259   $101.93   $101.95   $101.90  
  Purchase #5 $153.79   5.597%   $162.3976   $162.40   $162.40   $162.40  
  Purchase #6 $225.36   4.179%   $234.7778   $234.78   $234.80   $234.80  
  Purchase #7 $152.82   10.175%   $168.3694   $168.37   $168.35   $168.40  
  7 purchase totals = $1,221.69       $1,331.7859   $1,331.79   $1,331.80   $1,331.90