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 $201.49   6.301%   $214.1859   $214.19   $214.20   $214.20  
  Purchase #2 $152.51   8.169%   $164.9685   $164.97   $164.95   $165.00  
  Purchase #3 $51.97   4.357%   $54.2343   $54.23   $54.25   $54.20  
  Purchase #4 $57.67   9.243%   $63.0004   $63.00   $63.00   $63.00  
  Purchase #5 $243.35   10.748%   $269.5053   $269.51   $269.50   $269.50  
  Purchase #6 $179.86   8.285%   $194.7614   $194.76   $194.75   $194.80  
  Purchase #7 $135.32   5.671%   $142.994   $142.99   $143.00   $143.00  
  7 purchase totals = $1,022.17       $1,103.6498   $1,103.65   $1,103.65   $1,103.70