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 $90.66   12.193%   $101.7142   $101.71   $101.70   $101.70  
  Purchase #2 $82.71   9.655%   $90.6957   $90.70   $90.70   $90.70  
  Purchase #3 $247.41   8.566%   $268.6031   $268.60   $268.60   $268.60  
  Purchase #4 $213.89   8.491%   $232.0514   $232.05   $232.05   $232.10  
  Purchase #5 $238.59   11.789%   $266.7174   $266.72   $266.70   $266.70  
  Purchase #6 $226.26   6.513%   $240.9963   $241.00   $241.00   $241.00  
  Purchase #7 $133.82   7.355%   $143.6625   $143.66   $143.65   $143.70  
  7 purchase totals = $1,233.34       $1,344.4406   $1,344.44   $1,344.40   $1,344.50