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 $47.41   7.699%   $51.0601   $51.06   $51.05   $51.10  
  Purchase #2 $236.93   9.716%   $259.9501   $259.95   $259.95   $260.00  
  Purchase #3 $36.90   10.366%   $40.7251   $40.73   $40.75   $40.70  
  Purchase #4 $35.71   8.200%   $38.6382   $38.64   $38.65   $38.60  
  Purchase #5 $223.97   12.816%   $252.674   $252.67   $252.65   $252.70  
  Purchase #6 $30.73   4.585%   $32.139   $32.14   $32.15   $32.10  
  Purchase #7 $194.58   9.478%   $213.0223   $213.02   $213.00   $213.00  
  7 purchase totals = $806.23       $888.2088   $888.21   $888.20   $888.20