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 $111.25   13.653%   $126.439   $126.44   $126.45   $126.40  
  Purchase #2 $234.84   3.139%   $242.2116   $242.21   $242.20   $242.20  
  Purchase #3 $122.44   6.562%   $130.4745   $130.47   $130.45   $130.50  
  Purchase #4 $57.32   9.754%   $62.911   $62.91   $62.90   $62.90  
  Purchase #5 $213.75   13.652%   $242.9312   $242.93   $242.95   $242.90  
  Purchase #6 $127.56   8.638%   $138.5786   $138.58   $138.60   $138.60  
  Purchase #7 $73.73   8.480%   $79.9823   $79.98   $80.00   $80.00  
  7 purchase totals = $940.89       $1,023.5282   $1,023.52   $1,023.55   $1,023.50