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 $245.88   7.760%   $264.9603   $264.96   $264.95   $265.00  
  Purchase #2 $102.76   12.424%   $115.5269   $115.53   $115.55   $115.50  
  Purchase #3 $113.83   9.451%   $124.5881   $124.59   $124.60   $124.60  
  Purchase #4 $20.25   12.298%   $22.7403   $22.74   $22.75   $22.70  
  Purchase #5 $129.28   5.304%   $136.137   $136.14   $136.15   $136.10  
  Purchase #6 $25.58   3.150%   $26.3858   $26.39   $26.40   $26.40  
  Purchase #7 $235.81   3.609%   $244.3204   $244.32   $244.30   $244.30  
  7 purchase totals = $873.39       $934.6588   $934.67   $934.70   $934.60