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 $94.71   3.425%   $97.9538   $97.95   $97.95   $98.00  
  Purchase #2 $177.85   7.704%   $191.5516   $191.55   $191.55   $191.60  
  Purchase #3 $226.64   12.491%   $254.9496   $254.95   $254.95   $254.90  
  Purchase #4 $174.92   13.512%   $198.5552   $198.56   $198.55   $198.60  
  Purchase #5 $98.37   6.364%   $104.6303   $104.63   $104.65   $104.60  
  Purchase #6 $239.97   12.206%   $269.2607   $269.26   $269.25   $269.30  
  Purchase #7 $190.96   7.722%   $205.7059   $205.71   $205.70   $205.70  
  7 purchase totals = $1,203.42       $1,322.6071   $1,322.61   $1,322.60   $1,322.70