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 $184.39   8.190%   $199.4915   $199.49   $199.50   $199.50  
  Purchase #2 $201.54   8.348%   $218.3646   $218.36   $218.35   $218.40  
  Purchase #3 $195.83   11.673%   $218.6892   $218.69   $218.70   $218.70  
  Purchase #4 $228.90   5.557%   $241.62   $241.62   $241.60   $241.60  
  Purchase #5 $36.25   12.359%   $40.7301   $40.73   $40.75   $40.70  
  Purchase #6 $127.71   10.421%   $141.0187   $141.02   $141.00   $141.00  
  Purchase #7 $161.75   5.114%   $170.0219   $170.02   $170.00   $170.00  
  7 purchase totals = $1,136.37       $1,229.9360   $1,229.93   $1,229.90   $1,229.90