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 $34.47   5.558%   $36.3858   $36.39   $36.40   $36.40  
  Purchase #2 $146.43   13.235%   $165.81   $165.81   $165.80   $165.80  
  Purchase #3 $158.86   8.684%   $172.6554   $172.66   $172.65   $172.70  
  Purchase #4 $66.33   5.175%   $69.7626   $69.76   $69.75   $69.80  
  Purchase #5 $223.75   6.115%   $237.4323   $237.43   $237.45   $237.40  
  Purchase #6 $230.57   9.210%   $251.8055   $251.81   $251.80   $251.80  
  Purchase #7 $84.58   11.796%   $94.5571   $94.56   $94.55   $94.60  
  7 purchase totals = $944.99       $1,028.4087   $1,028.42   $1,028.40   $1,028.50