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 $60.30   13.794%   $68.6178   $68.62   $68.60   $68.60  
  Purchase #2 $101.52   12.149%   $113.8537   $113.85   $113.85   $113.90  
  Purchase #3 $113.25   6.778%   $120.9261   $120.93   $120.95   $120.90  
  Purchase #4 $152.36   3.284%   $157.3635   $157.36   $157.35   $157.40  
  Purchase #5 $58.90   11.103%   $65.4397   $65.44   $65.45   $65.40  
  Purchase #6 $14.34   9.829%   $15.7495   $15.75   $15.75   $15.70  
  Purchase #7 $116.99   12.540%   $131.6605   $131.66   $131.65   $131.70  
  7 purchase totals = $617.66       $673.6108   $673.61   $673.60   $673.60