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 $161.37   4.756%   $169.0448   $169.04   $169.05   $169.00  
  Purchase #2 $172.61   6.698%   $184.1714   $184.17   $184.15   $184.20  
  Purchase #3 $224.54   9.596%   $246.0869   $246.09   $246.10   $246.10  
  Purchase #4 $248.61   13.742%   $282.774   $282.77   $282.75   $282.80  
  Purchase #5 $127.86   4.448%   $133.5472   $133.55   $133.55   $133.50  
  Purchase #6 $248.76   4.125%   $259.0214   $259.02   $259.00   $259.00  
  Purchase #7 $210.84   7.760%   $227.2012   $227.20   $227.20   $227.20  
  7 purchase totals = $1,394.59       $1,501.8469   $1,501.84   $1,501.80   $1,501.80