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 $247.64   13.755%   $281.7029   $281.70   $281.70   $281.70  
  Purchase #2 $48.77   5.174%   $51.2934   $51.29   $51.30   $51.30  
  Purchase #3 $163.26   3.393%   $168.7994   $168.80   $168.80   $168.80  
  Purchase #4 $182.35   8.488%   $197.8279   $197.83   $197.85   $197.80  
  Purchase #5 $118.41   5.776%   $125.2494   $125.25   $125.25   $125.20  
  Purchase #6 $187.84   8.543%   $203.8872   $203.89   $203.90   $203.90  
  Purchase #7 $64.77   11.810%   $72.4193   $72.42   $72.40   $72.40  
  7 purchase totals = $1,013.04       $1,101.1795   $1,101.18   $1,101.20   $1,101.10