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 $33.43   3.476%   $34.592   $34.59   $34.60   $34.60  
  Purchase #2 $82.67   3.550%   $85.6048   $85.60   $85.60   $85.60  
  Purchase #3 $152.88   7.799%   $164.8031   $164.80   $164.80   $164.80  
  Purchase #4 $11.66   10.618%   $12.8981   $12.90   $12.90   $12.90  
  Purchase #5 $86.44   11.809%   $96.6477   $96.65   $96.65   $96.60  
  Purchase #6 $248.81   7.577%   $267.6623   $267.66   $267.65   $267.70  
  Purchase #7 $120.54   10.514%   $133.2136   $133.21   $133.20   $133.20  
  7 purchase totals = $736.43       $795.4216   $795.41   $795.40   $795.40