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 $86.26   12.231%   $96.8105   $96.81   $96.80   $96.80  
  Purchase #2 $115.80   12.503%   $130.2785   $130.28   $130.30   $130.30  
  Purchase #3 $246.79   4.274%   $257.3378   $257.34   $257.35   $257.30  
  Purchase #4 $210.57   12.298%   $236.4659   $236.47   $236.45   $236.50  
  Purchase #5 $121.65   8.198%   $131.6229   $131.62   $131.60   $131.60  
  Purchase #6 $205.31   12.830%   $231.6513   $231.65   $231.65   $231.70  
  Purchase #7 $75.86   8.636%   $82.4113   $82.41   $82.40   $82.40  
  7 purchase totals = $1,062.24       $1,166.5782   $1,166.58   $1,166.55   $1,166.60