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 $92.45   6.632%   $98.5813   $98.58   $98.60   $98.60  
  Purchase #2 $213.47   9.453%   $233.6493   $233.65   $233.65   $233.60  
  Purchase #3 $80.25   8.761%   $87.2807   $87.28   $87.30   $87.30  
  Purchase #4 $50.59   9.119%   $55.2033   $55.20   $55.20   $55.20  
  Purchase #5 $213.92   5.193%   $225.0289   $225.03   $225.05   $225.00  
  Purchase #6 $21.28   4.257%   $22.1859   $22.19   $22.20   $22.20  
  Purchase #7 $103.40   11.529%   $115.321   $115.32   $115.30   $115.30  
  7 purchase totals = $775.36       $837.2504   $837.25   $837.30   $837.20