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 $63.74   9.213%   $69.6124   $69.61   $69.60   $69.60  
  Purchase #2 $126.67   12.329%   $142.2871   $142.29   $142.30   $142.30  
  Purchase #3 $33.69   3.145%   $34.7496   $34.75   $34.75   $34.70  
  Purchase #4 $156.61   12.184%   $175.6914   $175.69   $175.70   $175.70  
  Purchase #5 $62.49   10.146%   $68.8302   $68.83   $68.85   $68.80  
  Purchase #6 $240.45   3.316%   $248.4233   $248.42   $248.40   $248.40  
  Purchase #7 $119.79   13.827%   $136.3534   $136.35   $136.35   $136.40  
  7 purchase totals = $803.44       $875.9474   $875.94   $875.95   $875.90