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 $221.41   13.331%   $250.9262   $250.93   $250.95   $250.90  
  Purchase #2 $41.66   6.786%   $44.487   $44.49   $44.50   $44.50  
  Purchase #3 $43.53   9.813%   $47.8016   $47.80   $47.80   $47.80  
  Purchase #4 $153.96   11.248%   $171.2774   $171.28   $171.30   $171.30  
  Purchase #5 $71.69   8.271%   $77.6195   $77.62   $77.60   $77.60  
  Purchase #6 $85.44   12.395%   $96.0303   $96.03   $96.05   $96.00  
  Purchase #7 $153.62   12.272%   $172.4722   $172.47   $172.45   $172.50  
  7 purchase totals = $771.31       $860.6142   $860.62   $860.65   $860.60