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 $237.40   11.753%   $265.3016   $265.30   $265.30   $265.30  
  Purchase #2 $238.28   5.655%   $251.7547   $251.75   $251.75   $251.80  
  Purchase #3 $136.44   10.202%   $150.3596   $150.36   $150.35   $150.40  
  Purchase #4 $191.93   12.184%   $215.3148   $215.31   $215.30   $215.30  
  Purchase #5 $210.43   12.379%   $236.4791   $236.48   $236.50   $236.50  
  Purchase #6 $30.36   6.516%   $32.3383   $32.34   $32.35   $32.30  
  Purchase #7 $106.69   4.619%   $111.618   $111.62   $111.60   $111.60  
  7 purchase totals = $1,151.53       $1,263.1661   $1,263.16   $1,263.15   $1,263.20