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 $54.41   6.469%   $57.9298   $57.93   $57.95   $57.90  
  Purchase #2 $71.79   6.103%   $76.1713   $76.17   $76.15   $76.20  
  Purchase #3 $112.59   4.317%   $117.4505   $117.45   $117.45   $117.50  
  Purchase #4 $158.56   3.184%   $163.6086   $163.61   $163.60   $163.60  
  Purchase #5 $126.82   3.689%   $131.4984   $131.50   $131.50   $131.50  
  Purchase #6 $56.69   10.566%   $62.6799   $62.68   $62.70   $62.70  
  Purchase #7 $141.67   5.867%   $149.9818   $149.98   $150.00   $150.00  
  7 purchase totals = $722.53       $759.3203   $759.32   $759.35   $759.40