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 $243.38   10.735%   $269.5068   $269.51   $269.50   $269.50  
  Purchase #2 $165.61   12.435%   $186.2036   $186.20   $186.20   $186.20  
  Purchase #3 $205.93   3.517%   $213.1726   $213.17   $213.15   $213.20  
  Purchase #4 $39.91   12.390%   $44.8548   $44.85   $44.85   $44.90  
  Purchase #5 $152.28   12.369%   $171.1155   $171.12   $171.10   $171.10  
  Purchase #6 $201.73   3.507%   $208.8047   $208.80   $208.80   $208.80  
  Purchase #7 $194.71   8.534%   $211.3266   $211.33   $211.35   $211.30  
  7 purchase totals = $1,203.55       $1,304.9846   $1,304.98   $1,304.95   $1,305.00