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 $93.88   8.123%   $101.5059   $101.51   $101.50   $101.50  
  Purchase #2 $184.37   12.361%   $207.16   $207.16   $207.15   $207.20  
  Purchase #3 $54.27   13.530%   $61.6127   $61.61   $61.60   $61.60  
  Purchase #4 $203.65   12.588%   $229.2855   $229.29   $229.30   $229.30  
  Purchase #5 $57.58   3.731%   $59.7283   $59.73   $59.75   $59.70  
  Purchase #6 $196.67   9.444%   $215.2435   $215.24   $215.25   $215.20  
  Purchase #7 $143.48   4.136%   $149.4143   $149.41   $149.40   $149.40  
  7 purchase totals = $933.90       $1,023.9502   $1,023.95   $1,023.95   $1,023.90