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 $55.64   9.571%   $60.9653   $60.97   $60.95   $61.00  
  Purchase #2 $241.55   9.159%   $263.6736   $263.67   $263.65   $263.70  
  Purchase #3 $120.81   9.701%   $132.5298   $132.53   $132.55   $132.50  
  Purchase #4 $222.51   9.780%   $244.2715   $244.27   $244.25   $244.30  
  Purchase #5 $30.94   13.159%   $35.0114   $35.01   $35.00   $35.00  
  Purchase #6 $67.80   8.477%   $73.5474   $73.55   $73.55   $73.50  
  Purchase #7 $192.64   11.538%   $214.8668   $214.87   $214.85   $214.90  
  7 purchase totals = $931.89       $1,024.8658   $1,024.87   $1,024.80   $1,024.90