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 $100.73   13.846%   $114.6771   $114.68   $114.70   $114.70  
  Purchase #2 $161.57   8.336%   $175.0385   $175.04   $175.05   $175.00  
  Purchase #3 $138.40   3.174%   $142.7928   $142.79   $142.80   $142.80  
  Purchase #4 $105.84   6.539%   $112.7609   $112.76   $112.75   $112.80  
  Purchase #5 $155.51   4.751%   $162.8983   $162.90   $162.90   $162.90  
  Purchase #6 $51.99   12.352%   $58.4118   $58.41   $58.40   $58.40  
  Purchase #7 $239.41   11.787%   $267.6293   $267.63   $267.65   $267.60  
  7 purchase totals = $953.45       $1,034.2087   $1,034.21   $1,034.25   $1,034.20