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 $114.74   6.580%   $122.2899   $122.29   $122.30   $122.30  
  Purchase #2 $246.56   6.588%   $262.8034   $262.80   $262.80   $262.80  
  Purchase #3 $214.42   4.151%   $223.3206   $223.32   $223.30   $223.30  
  Purchase #4 $91.60   13.303%   $103.7855   $103.79   $103.80   $103.80  
  Purchase #5 $43.91   8.295%   $47.5523   $47.55   $47.55   $47.60  
  Purchase #6 $152.56   13.669%   $173.4134   $173.41   $173.40   $173.40  
  Purchase #7 $222.25   12.550%   $250.1424   $250.14   $250.15   $250.10  
  7 purchase totals = $1,086.04       $1,183.3075   $1,183.30   $1,183.30   $1,183.30