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 $108.58   6.840%   $116.0069   $116.01   $116.00   $116.00  
  Purchase #2 $68.48   13.755%   $77.8994   $77.90   $77.90   $77.90  
  Purchase #3 $26.25   10.867%   $29.1026   $29.10   $29.10   $29.10  
  Purchase #4 $92.41   6.665%   $98.5691   $98.57   $98.55   $98.60  
  Purchase #5 $228.56   6.720%   $243.9192   $243.92   $243.90   $243.90  
  Purchase #6 $176.40   4.354%   $184.0805   $184.08   $184.10   $184.10  
  Purchase #7 $161.29   8.175%   $174.4755   $174.48   $174.50   $174.50  
  7 purchase totals = $861.97       $924.0532   $924.06   $924.05   $924.10