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 $40.27   9.209%   $43.9785   $43.98   $44.00   $44.00  
  Purchase #2 $60.86   7.838%   $65.6302   $65.63   $65.65   $65.60  
  Purchase #3 $147.69   5.591%   $155.9473   $155.95   $155.95   $155.90  
  Purchase #4 $41.33   11.185%   $45.9528   $45.95   $45.95   $46.00  
  Purchase #5 $10.89   3.790%   $11.3027   $11.30   $11.30   $11.30  
  Purchase #6 $196.84   9.655%   $215.8449   $215.84   $215.85   $215.80  
  Purchase #7 $32.83   3.604%   $34.0132   $34.01   $34.00   $34.00  
  7 purchase totals = $530.71       $572.6696   $572.66   $572.70   $572.60