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 $46.59   12.686%   $52.5004   $52.50   $52.50   $52.50  
  Purchase #2 $245.64   12.379%   $276.0478   $276.05   $276.05   $276.00  
  Purchase #3 $233.40   8.689%   $253.6801   $253.68   $253.70   $253.70  
  Purchase #4 $128.45   5.864%   $135.9823   $135.98   $136.00   $136.00  
  Purchase #5 $105.57   11.667%   $117.8869   $117.89   $117.90   $117.90  
  Purchase #6 $87.85   11.391%   $97.857   $97.86   $97.85   $97.90  
  Purchase #7 $149.63   8.666%   $162.5969   $162.60   $162.60   $162.60  
  7 purchase totals = $997.13       $1,096.5514   $1,096.56   $1,096.60   $1,096.60