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 $234.26   8.673%   $254.5774   $254.58   $254.60   $254.60  
  Purchase #2 $233.33   7.841%   $251.6254   $251.63   $251.65   $251.60  
  Purchase #3 $24.72   11.305%   $27.5146   $27.51   $27.50   $27.50  
  Purchase #4 $176.49   6.285%   $187.5824   $187.58   $187.60   $187.60  
  Purchase #5 $108.32   7.189%   $116.1071   $116.11   $116.10   $116.10  
  Purchase #6 $105.99   12.855%   $119.615   $119.62   $119.60   $119.60  
  Purchase #7 $51.57   11.411%   $57.4547   $57.45   $57.45   $57.50  
  7 purchase totals = $934.68       $1,014.4766   $1,014.48   $1,014.50   $1,014.50