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 $173.29   12.306%   $194.6151   $194.62   $194.60   $194.60  
  Purchase #2 $87.79   7.764%   $94.606   $94.61   $94.60   $94.60  
  Purchase #3 $184.39   9.564%   $202.0251   $202.03   $202.05   $202.00  
  Purchase #4 $18.66   6.359%   $19.8466   $19.85   $19.85   $19.80  
  Purchase #5 $218.26   8.538%   $236.895   $236.90   $236.90   $236.90  
  Purchase #6 $8.95   8.361%   $9.6983   $9.70   $9.70   $9.70  
  Purchase #7 $175.68   5.866%   $185.9854   $185.99   $186.00   $186.00  
  7 purchase totals = $867.02       $943.6715   $943.70   $943.70   $943.60