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 $47.91   8.370%   $51.9201   $51.92   $51.90   $51.90  
  Purchase #2 $132.38   10.754%   $146.6161   $146.62   $146.60   $146.60  
  Purchase #3 $66.72   12.168%   $74.8385   $74.84   $74.85   $74.80  
  Purchase #4 $239.33   7.437%   $257.129   $257.13   $257.15   $257.10  
  Purchase #5 $103.76   11.821%   $116.0255   $116.03   $116.05   $116.00  
  Purchase #6 $209.29   8.431%   $226.9352   $226.94   $226.95   $226.90  
  Purchase #7 $192.28   10.211%   $211.9137   $211.91   $211.90   $211.90  
  7 purchase totals = $991.67       $1,085.3781   $1,085.39   $1,085.40   $1,085.20