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 $42.35   12.603%   $47.6874   $47.69   $47.70   $47.70  
  Purchase #2 $98.72   6.294%   $104.9334   $104.93   $104.95   $104.90  
  Purchase #3 $208.97   8.756%   $227.2674   $227.27   $227.25   $227.30  
  Purchase #4 $212.72   9.809%   $233.5857   $233.59   $233.60   $233.60  
  Purchase #5 $156.97   11.645%   $175.2492   $175.25   $175.25   $175.20  
  Purchase #6 $155.84   10.501%   $172.2048   $172.20   $172.20   $172.20  
  Purchase #7 $247.34   13.242%   $280.0928   $280.09   $280.10   $280.10  
  7 purchase totals = $1,122.91       $1,241.0207   $1,241.02   $1,241.05   $1,241.00