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 $232.92   9.303%   $254.5885   $254.59   $254.60   $254.60  
  Purchase #2 $151.62   8.802%   $164.9656   $164.97   $164.95   $165.00  
  Purchase #3 $11.59   6.251%   $12.3145   $12.31   $12.30   $12.30  
  Purchase #4 $211.30   7.349%   $226.8284   $226.83   $226.85   $226.80  
  Purchase #5 $23.89   6.739%   $25.4999   $25.50   $25.50   $25.50  
  Purchase #6 $242.89   3.748%   $251.9935   $251.99   $252.00   $252.00  
  Purchase #7 $193.60   11.308%   $215.4923   $215.49   $215.50   $215.50  
  7 purchase totals = $1,067.81       $1,151.6827   $1,151.68   $1,151.70   $1,151.70