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 $61.30   11.862%   $68.5714   $68.57   $68.55   $68.60  
  Purchase #2 $121.96   3.259%   $125.9347   $125.93   $125.95   $125.90  
  Purchase #3 $151.55   10.425%   $167.3491   $167.35   $167.35   $167.30  
  Purchase #4 $141.32   5.539%   $149.1477   $149.15   $149.15   $149.10  
  Purchase #5 $86.57   11.233%   $96.2944   $96.29   $96.30   $96.30  
  Purchase #6 $230.31   5.712%   $243.4653   $243.47   $243.45   $243.50  
  Purchase #7 $90.25   13.136%   $102.1052   $102.11   $102.10   $102.10  
  7 purchase totals = $883.26       $952.8678   $952.87   $952.85   $952.80