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 $39.59   8.832%   $43.0866   $43.09   $43.10   $43.10  
  Purchase #2 $243.79   9.285%   $266.4259   $266.43   $266.45   $266.40  
  Purchase #3 $135.91   3.664%   $140.8897   $140.89   $140.90   $140.90  
  Purchase #4 $98.29   8.388%   $106.5346   $106.53   $106.55   $106.50  
  Purchase #5 $219.94   8.698%   $239.0704   $239.07   $239.05   $239.10  
  Purchase #6 $194.63   3.230%   $200.9165   $200.92   $200.90   $200.90  
  Purchase #7 $157.82   6.259%   $167.698   $167.70   $167.70   $167.70  
  7 purchase totals = $1,089.97       $1,164.6217   $1,164.63   $1,164.65   $1,164.60