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 $47.34   6.579%   $50.4545   $50.45   $50.45   $50.50  
  Purchase #2 $172.50   3.363%   $178.3012   $178.30   $178.30   $178.30  
  Purchase #3 $200.36   6.805%   $213.9945   $213.99   $214.00   $214.00  
  Purchase #4 $128.28   6.814%   $137.021   $137.02   $137.00   $137.00  
  Purchase #5 $229.68   5.533%   $242.3882   $242.39   $242.40   $242.40  
  Purchase #6 $189.72   6.696%   $202.4237   $202.42   $202.40   $202.40  
  Purchase #7 $168.88   13.707%   $192.0284   $192.03   $192.05   $192.00  
  7 purchase totals = $1,136.76       $1,216.6115   $1,216.60   $1,216.60   $1,216.60