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 $183.77   12.119%   $206.0411   $206.04   $206.05   $206.00  
  Purchase #2 $22.68   11.201%   $25.2204   $25.22   $25.20   $25.20  
  Purchase #3 $131.82   6.215%   $140.0126   $140.01   $140.00   $140.00  
  Purchase #4 $20.58   12.581%   $23.1692   $23.17   $23.15   $23.20  
  Purchase #5 $232.92   6.202%   $247.3657   $247.37   $247.35   $247.40  
  Purchase #6 $226.45   13.300%   $256.5679   $256.57   $256.55   $256.60  
  Purchase #7 $129.38   3.103%   $133.3947   $133.39   $133.40   $133.40  
  7 purchase totals = $947.60       $1,031.7716   $1,031.77   $1,031.70   $1,031.80