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 $237.96   11.795%   $266.0274   $266.03   $266.05   $266.00  
  Purchase #2 $93.32   5.649%   $98.5916   $98.59   $98.60   $98.60  
  Purchase #3 $192.89   9.161%   $210.5607   $210.56   $210.55   $210.60  
  Purchase #4 $152.70   8.533%   $165.7299   $165.73   $165.75   $165.70  
  Purchase #5 $217.45   8.137%   $235.1439   $235.14   $235.15   $235.10  
  Purchase #6 $34.81   10.655%   $38.519   $38.52   $38.50   $38.50  
  Purchase #7 $243.65   6.817%   $260.2596   $260.26   $260.25   $260.30  
  7 purchase totals = $1,172.78       $1,274.8321   $1,274.83   $1,274.85   $1,274.80