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 $54.86   8.861%   $59.7211   $59.72   $59.70   $59.70  
  Purchase #2 $121.98   4.612%   $127.6057   $127.61   $127.60   $127.60  
  Purchase #3 $175.68   10.660%   $194.4075   $194.41   $194.40   $194.40  
  Purchase #4 $152.68   6.286%   $162.2775   $162.28   $162.30   $162.30  
  Purchase #5 $112.44   4.766%   $117.7989   $117.80   $117.80   $117.80  
  Purchase #6 $163.81   6.818%   $174.9786   $174.98   $175.00   $175.00  
  Purchase #7 $70.73   8.571%   $76.7923   $76.79   $76.80   $76.80  
  7 purchase totals = $852.18       $913.5816   $913.59   $913.60   $913.60