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 $20.33   10.359%   $22.436   $22.44   $22.45   $22.40  
  Purchase #2 $61.90   7.691%   $66.6607   $66.66   $66.65   $66.70  
  Purchase #3 $242.25   6.629%   $258.3088   $258.31   $258.30   $258.30  
  Purchase #4 $220.66   3.652%   $228.7185   $228.72   $228.70   $228.70  
  Purchase #5 $202.40   6.851%   $216.2664   $216.27   $216.25   $216.30  
  Purchase #6 $93.72   7.339%   $100.5981   $100.60   $100.60   $100.60  
  Purchase #7 $193.29   8.874%   $210.4426   $210.44   $210.45   $210.40  
  7 purchase totals = $1,034.55       $1,103.4311   $1,103.44   $1,103.40   $1,103.40