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 $164.68   7.148%   $176.4513   $176.45   $176.45   $176.50  
  Purchase #2 $239.99   3.602%   $248.6344   $248.63   $248.65   $248.60  
  Purchase #3 $159.99   7.145%   $171.4213   $171.42   $171.40   $171.40  
  Purchase #4 $247.35   11.215%   $275.0903   $275.09   $275.10   $275.10  
  Purchase #5 $159.56   3.829%   $165.6696   $165.67   $165.65   $165.70  
  Purchase #6 $45.57   10.784%   $50.4843   $50.48   $50.50   $50.50  
  Purchase #7 $218.98   13.650%   $248.8708   $248.87   $248.85   $248.90  
  7 purchase totals = $1,236.12       $1,336.6220   $1,336.61   $1,336.60   $1,336.70