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 $51.91   6.794%   $55.4368   $55.44   $55.45   $55.40  
  Purchase #2 $153.44   10.596%   $169.6985   $169.70   $169.70   $169.70  
  Purchase #3 $88.39   5.159%   $92.95   $92.95   $92.95   $93.00  
  Purchase #4 $36.76   13.550%   $41.741   $41.74   $41.75   $41.70  
  Purchase #5 $247.94   10.130%   $273.0563   $273.06   $273.05   $273.10  
  Purchase #6 $109.88   7.517%   $118.1397   $118.14   $118.15   $118.10  
  Purchase #7 $16.61   9.402%   $18.1717   $18.17   $18.15   $18.20  
  7 purchase totals = $704.93       $769.1940   $769.20   $769.20   $769.20