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 $34.39   11.258%   $38.2616   $38.26   $38.25   $38.30  
  Purchase #2 $228.45   6.626%   $243.5871   $243.59   $243.60   $243.60  
  Purchase #3 $194.71   4.634%   $203.7329   $203.73   $203.75   $203.70  
  Purchase #4 $248.48   3.194%   $256.4165   $256.42   $256.40   $256.40  
  Purchase #5 $238.31   9.634%   $261.2688   $261.27   $261.25   $261.30  
  Purchase #6 $201.70   3.852%   $209.4695   $209.47   $209.45   $209.50  
  Purchase #7 $226.71   6.580%   $241.6275   $241.63   $241.65   $241.60  
  7 purchase totals = $1,372.75       $1,454.3639   $1,454.37   $1,454.35   $1,454.40