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 $245.98   3.342%   $254.2007   $254.20   $254.20   $254.20  
  Purchase #2 $57.63   13.499%   $65.4095   $65.41   $65.40   $65.40  
  Purchase #3 $157.64   6.835%   $168.4147   $168.41   $168.40   $168.40  
  Purchase #4 $156.53   3.801%   $162.4797   $162.48   $162.50   $162.50  
  Purchase #5 $247.36   7.325%   $265.4791   $265.48   $265.50   $265.50  
  Purchase #6 $224.85   8.587%   $244.1579   $244.16   $244.15   $244.20  
  Purchase #7 $240.43   13.373%   $272.5827   $272.58   $272.60   $272.60  
  7 purchase totals = $1,330.42       $1,432.7243   $1,432.72   $1,432.75   $1,432.80