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 $63.47   5.502%   $66.9621   $66.96   $66.95   $67.00  
  Purchase #2 $91.82   13.258%   $103.9935   $103.99   $104.00   $104.00  
  Purchase #3 $120.93   3.813%   $125.5411   $125.54   $125.55   $125.50  
  Purchase #4 $73.74   11.624%   $82.3115   $82.31   $82.30   $82.30  
  Purchase #5 $157.91   11.625%   $176.267   $176.27   $176.25   $176.30  
  Purchase #6 $156.69   13.531%   $177.8917   $177.89   $177.90   $177.90  
  Purchase #7 $106.95   6.122%   $113.4975   $113.50   $113.50   $113.50  
  7 purchase totals = $771.51       $846.4644   $846.46   $846.45   $846.50