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 $56.43   3.257%   $58.2679   $58.27   $58.25   $58.30  
  Purchase #2 $157.33   13.740%   $178.9471   $178.95   $178.95   $178.90  
  Purchase #3 $201.34   6.632%   $214.6929   $214.69   $214.70   $214.70  
  Purchase #4 $171.60   3.295%   $177.2542   $177.25   $177.25   $177.30  
  Purchase #5 $142.42   10.519%   $157.4012   $157.40   $157.40   $157.40  
  Purchase #6 $233.60   8.637%   $253.776   $253.78   $253.80   $253.80  
  Purchase #7 $90.99   6.627%   $97.0199   $97.02   $97.00   $97.00  
  7 purchase totals = $1,053.71       $1,137.3592   $1,137.36   $1,137.35   $1,137.40