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 $194.96   10.299%   $215.0389   $215.04   $215.05   $215.00  
  Purchase #2 $60.53   10.543%   $66.9117   $66.91   $66.90   $66.90  
  Purchase #3 $18.89   9.317%   $20.65   $20.65   $20.65   $20.70  
  Purchase #4 $216.54   7.705%   $233.2244   $233.22   $233.20   $233.20  
  Purchase #5 $44.39   10.312%   $48.9675   $48.97   $48.95   $49.00  
  Purchase #6 $216.70   12.124%   $242.9727   $242.97   $242.95   $243.00  
  Purchase #7 $121.62   10.856%   $134.8231   $134.82   $134.80   $134.80  
  7 purchase totals = $873.63       $962.5883   $962.58   $962.50   $962.60