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 $183.54   9.872%   $201.6591   $201.66   $201.65   $201.70  
  Purchase #2 $182.26   13.667%   $207.1695   $207.17   $207.15   $207.20  
  Purchase #3 $23.72   4.512%   $24.7902   $24.79   $24.80   $24.80  
  Purchase #4 $205.95   5.562%   $217.4049   $217.40   $217.40   $217.40  
  Purchase #5 $157.25   7.393%   $168.8755   $168.88   $168.90   $168.90  
  Purchase #6 $80.87   5.648%   $85.4375   $85.44   $85.45   $85.40  
  Purchase #7 $221.47   9.839%   $243.2604   $243.26   $243.25   $243.30  
  7 purchase totals = $1,055.06       $1,148.5971   $1,148.60   $1,148.60   $1,148.70