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 $207.54   13.228%   $234.9934   $234.99   $235.00   $235.00  
  Purchase #2 $82.56   12.330%   $92.7396   $92.74   $92.75   $92.70  
  Purchase #3 $226.94   7.843%   $244.7389   $244.74   $244.75   $244.70  
  Purchase #4 $77.85   10.621%   $86.1184   $86.12   $86.10   $86.10  
  Purchase #5 $203.88   6.369%   $216.8651   $216.87   $216.85   $216.90  
  Purchase #6 $159.87   10.577%   $176.7794   $176.78   $176.80   $176.80  
  Purchase #7 $162.85   8.243%   $176.2737   $176.27   $176.25   $176.30  
  7 purchase totals = $1,121.49       $1,228.5085   $1,228.51   $1,228.50   $1,228.50