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 $236.30   12.573%   $266.01   $266.01   $266.00   $266.00  
  Purchase #2 $76.64   7.685%   $82.5298   $82.53   $82.55   $82.50  
  Purchase #3 $48.87   7.348%   $52.461   $52.46   $52.45   $52.50  
  Purchase #4 $86.69   5.795%   $91.7137   $91.71   $91.70   $91.70  
  Purchase #5 $219.85   6.424%   $233.9732   $233.97   $233.95   $234.00  
  Purchase #6 $250.97   4.793%   $262.999   $263.00   $263.00   $263.00  
  Purchase #7 $10.54   13.615%   $11.975   $11.98   $12.00   $12.00  
  7 purchase totals = $929.86       $1,001.6617   $1,001.66   $1,001.65   $1,001.70