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 $168.37   8.847%   $183.2657   $183.27   $183.25   $183.30  
  Purchase #2 $220.42   6.820%   $235.4526   $235.45   $235.45   $235.50  
  Purchase #3 $177.87   12.294%   $199.7373   $199.74   $199.75   $199.70  
  Purchase #4 $177.51   13.804%   $202.0135   $202.01   $202.00   $202.00  
  Purchase #5 $62.90   13.424%   $71.3437   $71.34   $71.35   $71.30  
  Purchase #6 $147.58   8.325%   $159.866   $159.87   $159.85   $159.90  
  Purchase #7 $227.64   12.346%   $255.7444   $255.74   $255.75   $255.70  
  7 purchase totals = $1,182.29       $1,307.4232   $1,307.42   $1,307.40   $1,307.40