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 $58.63   8.729%   $63.7478   $63.75   $63.75   $63.70  
  Purchase #2 $37.58   3.683%   $38.9641   $38.96   $38.95   $39.00  
  Purchase #3 $52.84   12.641%   $59.5195   $59.52   $59.50   $59.50  
  Purchase #4 $10.45   10.621%   $11.5599   $11.56   $11.55   $11.60  
  Purchase #5 $111.74   3.778%   $115.9615   $115.96   $115.95   $116.00  
  Purchase #6 $43.46   10.342%   $47.9546   $47.95   $47.95   $48.00  
  Purchase #7 $250.28   5.863%   $264.9539   $264.95   $264.95   $265.00  
  7 purchase totals = $564.98       $602.6613   $602.65   $602.60   $602.80