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 $161.96   8.359%   $175.4982   $175.50   $175.50   $175.50  
  Purchase #2 $147.78   12.728%   $166.5894   $166.59   $166.60   $166.60  
  Purchase #3 $182.95   8.768%   $198.9911   $198.99   $199.00   $199.00  
  Purchase #4 $246.79   3.760%   $256.0693   $256.07   $256.05   $256.10  
  Purchase #5 $8.73   10.198%   $9.6203   $9.62   $9.60   $9.60  
  Purchase #6 $185.41   12.374%   $208.3526   $208.35   $208.35   $208.40  
  Purchase #7 $7.79   7.346%   $8.3623   $8.36   $8.35   $8.40  
  7 purchase totals = $941.41       $1,023.4832   $1,023.48   $1,023.45   $1,023.60