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 $202.37   10.340%   $223.2951   $223.30   $223.30   $223.30  
  Purchase #2 $227.87   3.348%   $235.4991   $235.50   $235.50   $235.50  
  Purchase #3 $107.60   9.605%   $117.935   $117.94   $117.95   $117.90  
  Purchase #4 $118.82   12.445%   $133.6071   $133.61   $133.60   $133.60  
  Purchase #5 $137.94   9.255%   $150.7063   $150.71   $150.70   $150.70  
  Purchase #6 $34.58   4.847%   $36.2561   $36.26   $36.25   $36.30  
  Purchase #7 $155.36   3.563%   $160.8955   $160.90   $160.90   $160.90  
  7 purchase totals = $984.54       $1,058.1942   $1,058.22   $1,058.20   $1,058.20