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 $59.76   13.228%   $67.6651   $67.67   $67.65   $67.70  
  Purchase #2 $243.92   4.466%   $254.8135   $254.81   $254.80   $254.80  
  Purchase #3 $59.92   12.856%   $67.6233   $67.62   $67.60   $67.60  
  Purchase #4 $189.40   6.224%   $201.1883   $201.19   $201.20   $201.20  
  Purchase #5 $64.45   13.739%   $73.3048   $73.30   $73.30   $73.30  
  Purchase #6 $63.84   4.793%   $66.8999   $66.90   $66.90   $66.90  
  Purchase #7 $14.60   9.218%   $15.9458   $15.95   $15.95   $15.90  
  7 purchase totals = $695.89       $747.4407   $747.44   $747.40   $747.40