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 $46.96   12.861%   $52.9995   $53.00   $53.00   $53.00  
  Purchase #2 $6.65   11.806%   $7.4351   $7.44   $7.45   $7.40  
  Purchase #3 $225.66   11.221%   $250.9813   $250.98   $251.00   $251.00  
  Purchase #4 $89.27   5.239%   $93.9469   $93.95   $93.95   $93.90  
  Purchase #5 $100.69   13.298%   $114.0798   $114.08   $114.10   $114.10  
  Purchase #6 $41.45   13.669%   $47.1158   $47.12   $47.10   $47.10  
  Purchase #7 $119.96   6.437%   $127.6818   $127.68   $127.70   $127.70  
  7 purchase totals = $630.64       $694.2402   $694.25   $694.30   $694.20