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 $93.29   13.464%   $105.8506   $105.85   $105.85   $105.90  
  Purchase #2 $197.26   6.348%   $209.7821   $209.78   $209.80   $209.80  
  Purchase #3 $146.48   13.574%   $166.3632   $166.36   $166.35   $166.40  
  Purchase #4 $101.25   5.872%   $107.1954   $107.20   $107.20   $107.20  
  Purchase #5 $243.90   11.705%   $272.4485   $272.45   $272.45   $272.40  
  Purchase #6 $46.89   9.534%   $51.3605   $51.36   $51.35   $51.40  
  Purchase #7 $44.67   11.735%   $49.912   $49.91   $49.90   $49.90  
  7 purchase totals = $873.74       $962.9123   $962.91   $962.90   $963.00