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 $170.71   11.324%   $190.0412   $190.04   $190.05   $190.00  
  Purchase #2 $95.42   8.536%   $103.5651   $103.57   $103.55   $103.60  
  Purchase #3 $157.58   4.664%   $164.9295   $164.93   $164.95   $164.90  
  Purchase #4 $201.67   9.272%   $220.3688   $220.37   $220.35   $220.40  
  Purchase #5 $166.32   12.202%   $186.6144   $186.61   $186.60   $186.60  
  Purchase #6 $127.67   5.871%   $135.1655   $135.17   $135.15   $135.20  
  Purchase #7 $187.36   10.188%   $206.4482   $206.45   $206.45   $206.40  
  7 purchase totals = $1,106.73       $1,207.1327   $1,207.14   $1,207.10   $1,207.10