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 $87.25   12.464%   $98.1248   $98.12   $98.10   $98.10  
  Purchase #2 $186.48   6.322%   $198.2693   $198.27   $198.25   $198.30  
  Purchase #3 $76.30   5.866%   $80.7758   $80.78   $80.80   $80.80  
  Purchase #4 $224.58   13.433%   $254.7478   $254.75   $254.75   $254.70  
  Purchase #5 $174.25   7.865%   $187.9548   $187.95   $187.95   $188.00  
  Purchase #6 $137.70   3.501%   $142.5209   $142.52   $142.50   $142.50  
  Purchase #7 $208.75   9.162%   $227.8757   $227.88   $227.90   $227.90  
  7 purchase totals = $1,095.31       $1,190.2691   $1,190.27   $1,190.25   $1,190.30