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 $63.42   6.609%   $67.6114   $67.61   $67.60   $67.60  
  Purchase #2 $32.64   3.160%   $33.6714   $33.67   $33.65   $33.70  
  Purchase #3 $249.45   9.238%   $272.4942   $272.49   $272.50   $272.50  
  Purchase #4 $228.45   7.761%   $246.18   $246.18   $246.20   $246.20  
  Purchase #5 $159.46   3.184%   $164.5372   $164.54   $164.55   $164.50  
  Purchase #6 $68.34   10.860%   $75.7617   $75.76   $75.75   $75.80  
  Purchase #7 $127.68   5.686%   $134.9399   $134.94   $134.95   $134.90  
  7 purchase totals = $929.44       $995.1958   $995.19   $995.20   $995.20