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 $106.53   6.770%   $113.7421   $113.74   $113.75   $113.70  
  Purchase #2 $199.42   9.113%   $217.5931   $217.59   $217.60   $217.60  
  Purchase #3 $217.77   8.601%   $236.5004   $236.50   $236.50   $236.50  
  Purchase #4 $106.52   8.333%   $115.3963   $115.40   $115.40   $115.40  
  Purchase #5 $190.97   12.541%   $214.9195   $214.92   $214.90   $214.90  
  Purchase #6 $77.84   9.861%   $85.5158   $85.52   $85.50   $85.50  
  Purchase #7 $58.52   3.530%   $60.5858   $60.59   $60.60   $60.60  
  7 purchase totals = $957.57       $1,044.2530   $1,044.26   $1,044.25   $1,044.20