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 $87.57   13.694%   $99.5618   $99.56   $99.55   $99.60  
  Purchase #2 $221.96   6.708%   $236.8491   $236.85   $236.85   $236.80  
  Purchase #3 $217.41   4.194%   $226.5282   $226.53   $226.55   $226.50  
  Purchase #4 $109.87   4.584%   $114.9064   $114.91   $114.90   $114.90  
  Purchase #5 $74.76   11.801%   $83.5824   $83.58   $83.60   $83.60  
  Purchase #6 $245.39   8.731%   $266.815   $266.82   $266.80   $266.80  
  Purchase #7 $81.25   9.256%   $88.7705   $88.77   $88.75   $88.80  
  7 purchase totals = $1,038.21       $1,117.0134   $1,117.02   $1,117.00   $1,117.00