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 $107.76   11.168%   $119.7946   $119.79   $119.80   $119.80  
  Purchase #2 $148.46   9.344%   $162.3321   $162.33   $162.35   $162.30  
  Purchase #3 $117.81   7.436%   $126.5704   $126.57   $126.55   $126.60  
  Purchase #4 $65.66   3.454%   $67.9279   $67.93   $67.95   $67.90  
  Purchase #5 $11.83   3.318%   $12.2225   $12.22   $12.20   $12.20  
  Purchase #6 $150.62   3.380%   $155.711   $155.71   $155.70   $155.70  
  Purchase #7 $155.95   4.180%   $162.4687   $162.47   $162.45   $162.50  
  7 purchase totals = $758.09       $807.0272   $807.02   $807.00   $807.00