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 $149.59   11.750%   $167.1668   $167.17   $167.15   $167.20  
  Purchase #2 $243.45   4.622%   $254.7023   $254.70   $254.70   $254.70  
  Purchase #3 $105.92   11.148%   $117.728   $117.73   $117.75   $117.70  
  Purchase #4 $14.80   10.754%   $16.3916   $16.39   $16.40   $16.40  
  Purchase #5 $170.27   3.670%   $176.5189   $176.52   $176.50   $176.50  
  Purchase #6 $93.67   13.551%   $106.3632   $106.36   $106.35   $106.40  
  Purchase #7 $6.73   10.689%   $7.4494   $7.45   $7.45   $7.40  
  7 purchase totals = $784.43       $846.3202   $846.32   $846.30   $846.30