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 $107.26   10.693%   $118.7293   $118.73   $118.75   $118.70  
  Purchase #2 $236.64   12.779%   $266.8802   $266.88   $266.90   $266.90  
  Purchase #3 $170.39   9.316%   $186.2635   $186.26   $186.25   $186.30  
  Purchase #4 $83.91   4.110%   $87.3587   $87.36   $87.35   $87.40  
  Purchase #5 $204.67   8.269%   $221.5942   $221.59   $221.60   $221.60  
  Purchase #6 $108.60   12.834%   $122.5377   $122.54   $122.55   $122.50  
  Purchase #7 $183.60   10.360%   $202.621   $202.62   $202.60   $202.60  
  7 purchase totals = $1,095.07       $1,205.9846   $1,205.98   $1,206.00   $1,206.00