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 $192.75   13.586%   $218.937   $218.94   $218.95   $218.90  
  Purchase #2 $119.44   5.773%   $126.3353   $126.34   $126.35   $126.30  
  Purchase #3 $241.62   9.247%   $263.9626   $263.96   $263.95   $264.00  
  Purchase #4 $22.79   12.330%   $25.6   $25.60   $25.60   $25.60  
  Purchase #5 $65.67   9.802%   $72.107   $72.11   $72.10   $72.10  
  Purchase #6 $186.73   7.159%   $200.098   $200.10   $200.10   $200.10  
  Purchase #7 $241.73   7.566%   $260.0193   $260.02   $260.00   $260.00  
  7 purchase totals = $1,070.73       $1,167.0592   $1,167.07   $1,167.05   $1,167.00