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 $218.48   10.318%   $241.0228   $241.02   $241.00   $241.00  
  Purchase #2 $68.64   10.282%   $75.6976   $75.70   $75.70   $75.70  
  Purchase #3 $173.49   5.171%   $182.4612   $182.46   $182.45   $182.50  
  Purchase #4 $143.60   5.262%   $151.1562   $151.16   $151.15   $151.20  
  Purchase #5 $238.61   9.807%   $262.0105   $262.01   $262.00   $262.00  
  Purchase #6 $171.43   13.760%   $195.0188   $195.02   $195.00   $195.00  
  Purchase #7 $161.99   8.804%   $176.2516   $176.25   $176.25   $176.30  
  7 purchase totals = $1,176.24       $1,283.6187   $1,283.62   $1,283.55   $1,283.70