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 $54.84   13.155%   $62.0542   $62.05   $62.05   $62.10  
  Purchase #2 $201.64   9.540%   $220.8765   $220.88   $220.90   $220.90  
  Purchase #3 $237.67   4.130%   $247.4858   $247.49   $247.50   $247.50  
  Purchase #4 $57.73   9.654%   $63.3033   $63.30   $63.30   $63.30  
  Purchase #5 $151.48   4.141%   $157.7528   $157.75   $157.75   $157.80  
  Purchase #6 $46.44   8.655%   $50.4594   $50.46   $50.45   $50.50  
  Purchase #7 $13.38   11.557%   $14.9263   $14.93   $14.95   $14.90  
  7 purchase totals = $763.18       $816.8583   $816.86   $816.90   $817.00