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 $234.85   13.583%   $266.7497   $266.75   $266.75   $266.70  
  Purchase #2 $114.90   13.483%   $130.392   $130.39   $130.40   $130.40  
  Purchase #3 $156.35   10.770%   $173.1889   $173.19   $173.20   $173.20  
  Purchase #4 $229.32   6.349%   $243.8795   $243.88   $243.90   $243.90  
  Purchase #5 $213.62   13.333%   $242.102   $242.10   $242.10   $242.10  
  Purchase #6 $95.53   13.370%   $108.3024   $108.30   $108.30   $108.30  
  Purchase #7 $66.99   7.809%   $72.2212   $72.22   $72.20   $72.20  
  7 purchase totals = $1,111.56       $1,236.8357   $1,236.83   $1,236.85   $1,236.80