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 $227.69   11.835%   $254.6371   $254.64   $254.65   $254.60  
  Purchase #2 $126.98   8.423%   $137.6755   $137.68   $137.70   $137.70  
  Purchase #3 $59.38   4.782%   $62.2196   $62.22   $62.20   $62.20  
  Purchase #4 $179.35   5.657%   $189.4958   $189.50   $189.50   $189.50  
  Purchase #5 $85.49   10.635%   $94.5819   $94.58   $94.60   $94.60  
  Purchase #6 $131.32   12.827%   $148.1644   $148.16   $148.15   $148.20  
  Purchase #7 $119.81   10.361%   $132.2235   $132.22   $132.20   $132.20  
  7 purchase totals = $930.02       $1,018.9978   $1,019.00   $1,019.00   $1,019.00