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 $214.60   12.303%   $241.0022   $241.00   $241.00   $241.00  
  Purchase #2 $240.66   11.737%   $268.9063   $268.91   $268.90   $268.90  
  Purchase #3 $163.65   7.665%   $176.1938   $176.19   $176.20   $176.20  
  Purchase #4 $243.84   10.384%   $269.1603   $269.16   $269.15   $269.20  
  Purchase #5 $179.91   6.496%   $191.597   $191.60   $191.60   $191.60  
  Purchase #6 $31.99   7.674%   $34.4449   $34.44   $34.45   $34.40  
  Purchase #7 $5.66   6.313%   $6.0173   $6.02   $6.00   $6.00  
  7 purchase totals = $1,080.31       $1,187.3218   $1,187.32   $1,187.30   $1,187.30