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 $84.79   11.619%   $94.6418   $94.64   $94.65   $94.60  
  Purchase #2 $118.39   7.536%   $127.3119   $127.31   $127.30   $127.30  
  Purchase #3 $207.76   6.503%   $221.2706   $221.27   $221.25   $221.30  
  Purchase #4 $185.27   12.194%   $207.8618   $207.86   $207.85   $207.90  
  Purchase #5 $74.99   13.382%   $85.0252   $85.03   $85.05   $85.00  
  Purchase #6 $147.55   4.487%   $154.1706   $154.17   $154.15   $154.20  
  Purchase #7 $143.97   5.572%   $151.992   $151.99   $152.00   $152.00  
  7 purchase totals = $962.72       $1,042.2739   $1,042.27   $1,042.25   $1,042.30