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 $62.51   10.199%   $68.8854   $68.89   $68.90   $68.90  
  Purchase #2 $176.50   9.457%   $193.1916   $193.19   $193.20   $193.20  
  Purchase #3 $5.29   12.797%   $5.967   $5.97   $5.95   $6.00  
  Purchase #4 $109.29   13.855%   $124.4321   $124.43   $124.45   $124.40  
  Purchase #5 $53.91   10.338%   $59.4832   $59.48   $59.50   $59.50  
  Purchase #6 $208.80   3.598%   $216.3126   $216.31   $216.30   $216.30  
  Purchase #7 $41.97   12.223%   $47.1   $47.10   $47.10   $47.10  
  7 purchase totals = $658.27       $715.3719   $715.37   $715.40   $715.40