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 $224.57   8.521%   $243.7056   $243.71   $243.70   $243.70  
  Purchase #2 $250.57   4.496%   $261.8356   $261.84   $261.85   $261.80  
  Purchase #3 $178.81   4.163%   $186.2539   $186.25   $186.25   $186.30  
  Purchase #4 $201.74   9.436%   $220.7762   $220.78   $220.80   $220.80  
  Purchase #5 $78.53   8.852%   $85.4815   $85.48   $85.50   $85.50  
  Purchase #6 $119.64   12.792%   $134.9443   $134.94   $134.95   $134.90  
  Purchase #7 $17.65   9.339%   $19.2983   $19.30   $19.30   $19.30  
  7 purchase totals = $1,071.51       $1,152.2954   $1,152.30   $1,152.35   $1,152.30