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 $24.52   6.104%   $26.0167   $26.02   $26.00   $26.00  
  Purchase #2 $138.37   10.682%   $153.1507   $153.15   $153.15   $153.20  
  Purchase #3 $213.39   12.318%   $239.6754   $239.68   $239.70   $239.70  
  Purchase #4 $67.42   12.266%   $75.6897   $75.69   $75.70   $75.70  
  Purchase #5 $29.33   10.676%   $32.4613   $32.46   $32.45   $32.50  
  Purchase #6 $67.76   3.786%   $70.3254   $70.33   $70.35   $70.30  
  Purchase #7 $130.91   10.744%   $144.975   $144.98   $145.00   $145.00  
  7 purchase totals = $671.70       $742.2942   $742.31   $742.35   $742.40