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 $59.37   13.824%   $67.5773   $67.58   $67.60   $67.60  
  Purchase #2 $61.45   8.511%   $66.68   $66.68   $66.70   $66.70  
  Purchase #3 $111.74   5.645%   $118.0477   $118.05   $118.05   $118.00  
  Purchase #4 $116.33   8.775%   $126.538   $126.54   $126.55   $126.50  
  Purchase #5 $132.95   10.693%   $147.1663   $147.17   $147.15   $147.20  
  Purchase #6 $99.37   12.834%   $112.1231   $112.12   $112.10   $112.10  
  Purchase #7 $135.52   9.360%   $148.2047   $148.20   $148.20   $148.20  
  7 purchase totals = $716.73       $786.3371   $786.34   $786.35   $786.30