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 $123.59   4.849%   $129.5829   $129.58   $129.60   $129.60  
  Purchase #2 $189.93   7.335%   $203.8614   $203.86   $203.85   $203.90  
  Purchase #3 $236.55   11.179%   $262.9939   $262.99   $263.00   $263.00  
  Purchase #4 $227.76   9.663%   $249.7684   $249.77   $249.75   $249.80  
  Purchase #5 $220.27   8.570%   $239.1471   $239.15   $239.15   $239.10  
  Purchase #6 $84.81   12.819%   $95.6818   $95.68   $95.70   $95.70  
  Purchase #7 $172.66   6.128%   $183.2406   $183.24   $183.25   $183.20  
  7 purchase totals = $1,255.57       $1,364.2761   $1,364.27   $1,364.30   $1,364.30