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 $233.39   12.652%   $262.9185   $262.92   $262.90   $262.90  
  Purchase #2 $62.98   6.116%   $66.8319   $66.83   $66.85   $66.80  
  Purchase #3 $106.99   11.260%   $119.0371   $119.04   $119.05   $119.00  
  Purchase #4 $170.29   10.801%   $188.683   $188.68   $188.70   $188.70  
  Purchase #5 $124.97   5.257%   $131.5397   $131.54   $131.55   $131.50  
  Purchase #6 $46.68   6.586%   $49.7543   $49.75   $49.75   $49.80  
  Purchase #7 $59.31   12.557%   $66.7576   $66.76   $66.75   $66.80  
  7 purchase totals = $804.61       $885.5221   $885.52   $885.55   $885.50