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 $57.33   8.524%   $62.2168   $62.22   $62.20   $62.20  
  Purchase #2 $71.96   9.716%   $78.9516   $78.95   $78.95   $79.00  
  Purchase #3 $45.87   7.437%   $49.2814   $49.28   $49.30   $49.30  
  Purchase #4 $24.71   10.790%   $27.3762   $27.38   $27.40   $27.40  
  Purchase #5 $49.66   11.572%   $55.4067   $55.41   $55.40   $55.40  
  Purchase #6 $105.33   9.430%   $115.2626   $115.26   $115.25   $115.30  
  Purchase #7 $66.66   8.654%   $72.4288   $72.43   $72.45   $72.40  
  7 purchase totals = $421.52       $460.9241   $460.93   $460.95   $461.00