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 $59.34   5.256%   $62.4589   $62.46   $62.45   $62.50  
  Purchase #2 $131.35   8.752%   $142.8458   $142.85   $142.85   $142.80  
  Purchase #3 $209.82   8.373%   $227.3882   $227.39   $227.40   $227.40  
  Purchase #4 $221.64   8.751%   $241.0357   $241.04   $241.05   $241.00  
  Purchase #5 $246.66   10.197%   $271.8119   $271.81   $271.80   $271.80  
  Purchase #6 $45.47   4.202%   $47.3806   $47.38   $47.40   $47.40  
  Purchase #7 $7.84   5.307%   $8.2561   $8.26   $8.25   $8.30  
  7 purchase totals = $922.12       $1,001.1772   $1,001.19   $1,001.20   $1,001.20