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 $59.86   9.696%   $65.664   $65.66   $65.65   $65.70  
  Purchase #2 $58.35   3.852%   $60.5976   $60.60   $60.60   $60.60  
  Purchase #3 $210.46   8.704%   $228.7784   $228.78   $228.80   $228.80  
  Purchase #4 $14.32   11.854%   $16.0175   $16.02   $16.00   $16.00  
  Purchase #5 $234.58   4.423%   $244.9555   $244.96   $244.95   $245.00  
  Purchase #6 $48.58   4.276%   $50.6573   $50.66   $50.65   $50.70  
  Purchase #7 $210.78   3.198%   $217.5207   $217.52   $217.50   $217.50  
  7 purchase totals = $836.93       $884.1910   $884.20   $884.15   $884.30