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 $198.97   13.185%   $225.2042   $225.20   $225.20   $225.20  
  Purchase #2 $179.64   3.334%   $185.6292   $185.63   $185.65   $185.60  
  Purchase #3 $187.69   4.135%   $195.451   $195.45   $195.45   $195.50  
  Purchase #4 $221.89   6.261%   $235.7825   $235.78   $235.80   $235.80  
  Purchase #5 $59.66   6.398%   $63.477   $63.48   $63.50   $63.50  
  Purchase #6 $45.92   3.469%   $47.513   $47.51   $47.50   $47.50  
  Purchase #7 $144.95   7.783%   $156.2315   $156.23   $156.25   $156.20  
  7 purchase totals = $1,038.72       $1,109.2884   $1,109.28   $1,109.35   $1,109.30