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 $180.61   11.858%   $202.0267   $202.03   $202.05   $202.00  
  Purchase #2 $118.58   8.700%   $128.8965   $128.90   $128.90   $128.90  
  Purchase #3 $171.36   5.860%   $181.4017   $181.40   $181.40   $181.40  
  Purchase #4 $169.63   3.853%   $176.1658   $176.17   $176.15   $176.20  
  Purchase #5 $224.30   7.672%   $241.5083   $241.51   $241.50   $241.50  
  Purchase #6 $91.38   4.276%   $95.2874   $95.29   $95.30   $95.30  
  Purchase #7 $51.77   13.168%   $58.5871   $58.59   $58.60   $58.60  
  7 purchase totals = $1,007.63       $1,083.8735   $1,083.89   $1,083.90   $1,083.90