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 $49.77   11.667%   $55.5767   $55.58   $55.60   $55.60  
  Purchase #2 $200.42   11.281%   $223.0294   $223.03   $223.05   $223.00  
  Purchase #3 $34.46   5.692%   $36.4215   $36.42   $36.40   $36.40  
  Purchase #4 $49.27   11.340%   $54.8572   $54.86   $54.85   $54.90  
  Purchase #5 $58.92   10.540%   $65.1302   $65.13   $65.15   $65.10  
  Purchase #6 $233.84   12.131%   $262.2071   $262.21   $262.20   $262.20  
  Purchase #7 $117.74   12.198%   $132.1019   $132.10   $132.10   $132.10  
  7 purchase totals = $744.42       $829.3240   $829.33   $829.35   $829.30