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 $207.82   12.592%   $233.9887   $233.99   $234.00   $234.00  
  Purchase #2 $192.86   10.639%   $213.3784   $213.38   $213.40   $213.40  
  Purchase #3 $61.88   9.494%   $67.7549   $67.75   $67.75   $67.80  
  Purchase #4 $115.77   6.213%   $122.9628   $122.96   $122.95   $123.00  
  Purchase #5 $23.65   13.183%   $26.7678   $26.77   $26.75   $26.80  
  Purchase #6 $243.25   13.161%   $275.2641   $275.26   $275.25   $275.30  
  Purchase #7 $66.54   10.816%   $73.737   $73.74   $73.75   $73.70  
  7 purchase totals = $911.77       $1,013.8537   $1,013.85   $1,013.85   $1,014.00