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 $204.38   11.706%   $228.3047   $228.30   $228.30   $228.30  
  Purchase #2 $247.26   12.359%   $277.8189   $277.82   $277.80   $277.80  
  Purchase #3 $34.95   5.431%   $36.8481   $36.85   $36.85   $36.80  
  Purchase #4 $17.91   9.383%   $19.5905   $19.59   $19.60   $19.60  
  Purchase #5 $87.42   7.799%   $94.2379   $94.24   $94.25   $94.20  
  Purchase #6 $239.26   12.794%   $269.8709   $269.87   $269.85   $269.90  
  Purchase #7 $228.92   13.247%   $259.245   $259.25   $259.25   $259.20  
  7 purchase totals = $1,060.10       $1,185.9160   $1,185.92   $1,185.90   $1,185.80