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 $235.91   6.312%   $250.8006   $250.80   $250.80   $250.80  
  Purchase #2 $56.99   7.502%   $61.2654   $61.27   $61.25   $61.30  
  Purchase #3 $41.87   6.498%   $44.5907   $44.59   $44.60   $44.60  
  Purchase #4 $106.87   6.654%   $113.9811   $113.98   $114.00   $114.00  
  Purchase #5 $32.87   4.533%   $34.36   $34.36   $34.35   $34.40  
  Purchase #6 $126.78   12.342%   $142.4272   $142.43   $142.45   $142.40  
  Purchase #7 $100.39   9.416%   $109.8427   $109.84   $109.85   $109.80  
  7 purchase totals = $701.68       $757.2677   $757.27   $757.30   $757.30