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 $30.49   10.452%   $33.6768   $33.68   $33.70   $33.70  
  Purchase #2 $178.86   9.320%   $195.5298   $195.53   $195.55   $195.50  
  Purchase #3 $178.26   11.503%   $198.7652   $198.77   $198.75   $198.80  
  Purchase #4 $223.79   5.608%   $236.3401   $236.34   $236.35   $236.30  
  Purchase #5 $104.43   13.760%   $118.7996   $118.80   $118.80   $118.80  
  Purchase #6 $173.25   12.593%   $195.0674   $195.07   $195.05   $195.10  
  Purchase #7 $151.86   6.609%   $161.8964   $161.90   $161.90   $161.90  
  7 purchase totals = $1,040.94       $1,140.0753   $1,140.09   $1,140.10   $1,140.10