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 $117.26   6.175%   $124.5008   $124.50   $124.50   $124.50  
  Purchase #2 $166.73   6.612%   $177.7542   $177.75   $177.75   $177.80  
  Purchase #3 $68.53   6.306%   $72.8515   $72.85   $72.85   $72.90  
  Purchase #4 $39.36   6.504%   $41.92   $41.92   $41.90   $41.90  
  Purchase #5 $104.25   9.552%   $114.208   $114.21   $114.20   $114.20  
  Purchase #6 $212.92   13.601%   $241.8792   $241.88   $241.90   $241.90  
  Purchase #7 $210.75   4.776%   $220.8154   $220.82   $220.80   $220.80  
  7 purchase totals = $919.80       $993.9291   $993.93   $993.90   $994.00