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 $120.80   9.275%   $132.0042   $132.00   $132.00   $132.00  
  Purchase #2 $243.41   9.598%   $266.7725   $266.77   $266.75   $266.80  
  Purchase #3 $165.49   7.712%   $178.2526   $178.25   $178.25   $178.30  
  Purchase #4 $175.99   5.453%   $185.5867   $185.59   $185.60   $185.60  
  Purchase #5 $186.50   9.386%   $204.0049   $204.00   $204.00   $204.00  
  Purchase #6 $212.76   11.651%   $237.5487   $237.55   $237.55   $237.50  
  Purchase #7 $183.25   4.305%   $191.1389   $191.14   $191.15   $191.10  
  7 purchase totals = $1,288.20       $1,395.3085   $1,395.30   $1,395.30   $1,395.30