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 $58.98   8.248%   $63.8447   $63.84   $63.85   $63.80  
  Purchase #2 $56.58   10.152%   $62.324   $62.32   $62.30   $62.30  
  Purchase #3 $50.28   4.667%   $52.6266   $52.63   $52.65   $52.60  
  Purchase #4 $166.27   10.558%   $183.8248   $183.82   $183.80   $183.80  
  Purchase #5 $60.52   5.528%   $63.8655   $63.87   $63.85   $63.90  
  Purchase #6 $189.38   11.313%   $210.8046   $210.80   $210.80   $210.80  
  Purchase #7 $176.62   5.656%   $186.6096   $186.61   $186.60   $186.60  
  7 purchase totals = $758.63       $823.8998   $823.89   $823.85   $823.80