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 $232.99   4.728%   $244.0058   $244.01   $244.00   $244.00  
  Purchase #2 $105.61   9.759%   $115.9165   $115.92   $115.90   $115.90  
  Purchase #3 $250.76   7.333%   $269.1482   $269.15   $269.15   $269.10  
  Purchase #4 $152.56   11.633%   $170.3073   $170.31   $170.30   $170.30  
  Purchase #5 $70.80   12.404%   $79.582   $79.58   $79.60   $79.60  
  Purchase #6 $182.79   12.597%   $205.8161   $205.82   $205.80   $205.80  
  Purchase #7 $156.86   9.825%   $172.2715   $172.27   $172.25   $172.30  
  7 purchase totals = $1,152.37       $1,257.0474   $1,257.06   $1,257.00   $1,257.00