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 $159.25   3.791%   $165.2872   $165.29   $165.30   $165.30  
  Purchase #2 $39.37   5.784%   $41.6472   $41.65   $41.65   $41.60  
  Purchase #3 $195.89   3.314%   $202.3818   $202.38   $202.40   $202.40  
  Purchase #4 $115.96   7.746%   $124.9423   $124.94   $124.95   $124.90  
  Purchase #5 $174.81   11.335%   $194.6247   $194.62   $194.60   $194.60  
  Purchase #6 $248.61   4.425%   $259.611   $259.61   $259.60   $259.60  
  Purchase #7 $35.72   4.785%   $37.4292   $37.43   $37.45   $37.40  
  7 purchase totals = $969.61       $1,025.9234   $1,025.92   $1,025.95   $1,025.80