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 $89.60   4.751%   $93.8569   $93.86   $93.85   $93.90  
  Purchase #2 $66.81   3.283%   $69.0034   $69.00   $69.00   $69.00  
  Purchase #3 $169.39   4.230%   $176.5552   $176.56   $176.55   $176.60  
  Purchase #4 $134.85   4.330%   $140.689   $140.69   $140.70   $140.70  
  Purchase #5 $188.61   4.576%   $197.2408   $197.24   $197.25   $197.20  
  Purchase #6 $131.37   3.430%   $135.876   $135.88   $135.90   $135.90  
  Purchase #7 $27.68   5.768%   $29.2766   $29.28   $29.30   $29.30  
  7 purchase totals = $808.31       $842.4979   $842.51   $842.55   $842.60