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 $116.31   6.204%   $123.5259   $123.53   $123.55   $123.50  
  Purchase #2 $93.32   9.247%   $101.9493   $101.95   $101.95   $101.90  
  Purchase #3 $37.91   9.535%   $41.5247   $41.52   $41.50   $41.50  
  Purchase #4 $234.88   11.787%   $262.5653   $262.57   $262.55   $262.60  
  Purchase #5 $40.96   6.520%   $43.6306   $43.63   $43.65   $43.60  
  Purchase #6 $222.37   13.459%   $252.2988   $252.30   $252.30   $252.30  
  Purchase #7 $164.73   5.195%   $173.2877   $173.29   $173.30   $173.30  
  7 purchase totals = $910.48       $998.7823   $998.79   $998.80   $998.70