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 $82.44   13.173%   $93.2998   $93.30   $93.30   $93.30  
  Purchase #2 $207.95   12.467%   $233.8751   $233.88   $233.90   $233.90  
  Purchase #3 $26.51   12.463%   $29.8139   $29.81   $29.80   $29.80  
  Purchase #4 $82.87   5.152%   $87.1395   $87.14   $87.15   $87.10  
  Purchase #5 $124.83   12.707%   $140.6921   $140.69   $140.70   $140.70  
  Purchase #6 $213.61   5.345%   $225.0275   $225.03   $225.05   $225.00  
  Purchase #7 $211.88   10.273%   $233.6464   $233.65   $233.65   $233.60  
  7 purchase totals = $950.09       $1,043.4943   $1,043.50   $1,043.55   $1,043.40