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 $55.44   11.552%   $61.8444   $61.84   $61.85   $61.80  
  Purchase #2 $72.75   12.401%   $81.7717   $81.77   $81.75   $81.80  
  Purchase #3 $79.38   5.332%   $83.6125   $83.61   $83.60   $83.60  
  Purchase #4 $163.80   6.210%   $173.972   $173.97   $173.95   $174.00  
  Purchase #5 $183.69   5.305%   $193.4348   $193.43   $193.45   $193.40  
  Purchase #6 $223.28   7.171%   $239.2914   $239.29   $239.30   $239.30  
  Purchase #7 $57.70   3.620%   $59.7887   $59.79   $59.80   $59.80  
  7 purchase totals = $836.04       $893.7155   $893.70   $893.70   $893.70