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 $207.64   12.482%   $233.5576   $233.56   $233.55   $233.60  
  Purchase #2 $96.25   7.322%   $103.2974   $103.30   $103.30   $103.30  
  Purchase #3 $115.55   12.213%   $129.6621   $129.66   $129.65   $129.70  
  Purchase #4 $62.94   3.561%   $65.1813   $65.18   $65.20   $65.20  
  Purchase #5 $181.70   9.509%   $198.9779   $198.98   $199.00   $199.00  
  Purchase #6 $52.89   4.512%   $55.2764   $55.28   $55.30   $55.30  
  Purchase #7 $221.28   8.699%   $240.5291   $240.53   $240.55   $240.50  
  7 purchase totals = $938.25       $1,026.4818   $1,026.49   $1,026.55   $1,026.60