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 $90.77   5.719%   $95.9611   $95.96   $95.95   $96.00  
  Purchase #2 $230.79   6.842%   $246.5807   $246.58   $246.60   $246.60  
  Purchase #3 $74.46   9.843%   $81.7891   $81.79   $81.80   $81.80  
  Purchase #4 $57.33   11.529%   $63.9396   $63.94   $63.95   $63.90  
  Purchase #5 $149.41   10.850%   $165.621   $165.62   $165.60   $165.60  
  Purchase #6 $20.75   3.383%   $21.452   $21.45   $21.45   $21.50  
  Purchase #7 $241.96   13.499%   $274.6222   $274.62   $274.60   $274.60  
  7 purchase totals = $865.47       $949.9657   $949.96   $949.95   $950.00