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 $55.88   6.629%   $59.5843   $59.58   $59.60   $59.60  
  Purchase #2 $227.88   7.205%   $244.2988   $244.30   $244.30   $244.30  
  Purchase #3 $57.29   4.196%   $59.6939   $59.69   $59.70   $59.70  
  Purchase #4 $55.43   5.637%   $58.5546   $58.55   $58.55   $58.60  
  Purchase #5 $216.80   7.391%   $232.8237   $232.82   $232.80   $232.80  
  Purchase #6 $20.58   12.679%   $23.1893   $23.19   $23.20   $23.20  
  Purchase #7 $49.38   4.410%   $51.5577   $51.56   $51.55   $51.60  
  7 purchase totals = $683.24       $729.7023   $729.69   $729.70   $729.80