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 $194.33   6.721%   $207.3909   $207.39   $207.40   $207.40  
  Purchase #2 $152.79   10.799%   $169.2898   $169.29   $169.30   $169.30  
  Purchase #3 $33.89   6.834%   $36.206   $36.21   $36.20   $36.20  
  Purchase #4 $76.48   6.210%   $81.2294   $81.23   $81.25   $81.20  
  Purchase #5 $131.57   8.180%   $142.3324   $142.33   $142.35   $142.30  
  Purchase #6 $231.87   6.736%   $247.4888   $247.49   $247.50   $247.50  
  Purchase #7 $11.79   6.778%   $12.5891   $12.59   $12.60   $12.60  
  7 purchase totals = $832.72       $896.5264   $896.53   $896.60   $896.50