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 $162.72   12.593%   $183.2113   $183.21   $183.20   $183.20  
  Purchase #2 $59.64   6.622%   $63.5894   $63.59   $63.60   $63.60  
  Purchase #3 $68.56   3.115%   $70.6956   $70.70   $70.70   $70.70  
  Purchase #4 $141.45   10.322%   $156.0505   $156.05   $156.05   $156.10  
  Purchase #5 $201.69   13.197%   $228.307   $228.31   $228.30   $228.30  
  Purchase #6 $21.91   6.477%   $23.3291   $23.33   $23.35   $23.30  
  Purchase #7 $218.28   10.687%   $241.6076   $241.61   $241.60   $241.60  
  7 purchase totals = $874.25       $966.7905   $966.80   $966.80   $966.80