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 $208.47   13.288%   $236.1715   $236.17   $236.15   $236.20  
  Purchase #2 $103.79   4.583%   $108.5467   $108.55   $108.55   $108.50  
  Purchase #3 $115.31   4.368%   $120.3467   $120.35   $120.35   $120.30  
  Purchase #4 $234.88   3.332%   $242.7062   $242.71   $242.70   $242.70  
  Purchase #5 $104.59   11.172%   $116.2748   $116.27   $116.25   $116.30  
  Purchase #6 $132.71   7.514%   $142.6818   $142.68   $142.70   $142.70  
  Purchase #7 $74.33   4.261%   $77.4972   $77.50   $77.50   $77.50  
  7 purchase totals = $974.08       $1,044.2249   $1,044.23   $1,044.20   $1,044.20