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 $228.41   11.207%   $254.0079   $254.01   $254.00   $254.00  
  Purchase #2 $200.78   6.574%   $213.9793   $213.98   $214.00   $214.00  
  Purchase #3 $188.83   11.201%   $209.9808   $209.98   $210.00   $210.00  
  Purchase #4 $159.59   11.699%   $178.2604   $178.26   $178.25   $178.30  
  Purchase #5 $195.66   9.422%   $214.0951   $214.10   $214.10   $214.10  
  Purchase #6 $247.45   5.711%   $261.5819   $261.58   $261.60   $261.60  
  Purchase #7 $169.87   6.541%   $180.9812   $180.98   $181.00   $181.00  
  7 purchase totals = $1,390.59       $1,512.8866   $1,512.89   $1,512.95   $1,513.00