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 $90.84   5.176%   $95.5419   $95.54   $95.55   $95.50  
  Purchase #2 $219.43   3.182%   $226.4123   $226.41   $226.40   $226.40  
  Purchase #3 $242.25   6.249%   $257.3882   $257.39   $257.40   $257.40  
  Purchase #4 $192.43   8.576%   $208.9328   $208.93   $208.95   $208.90  
  Purchase #5 $102.36   12.504%   $115.1591   $115.16   $115.15   $115.20  
  Purchase #6 $67.27   11.812%   $75.2159   $75.22   $75.20   $75.20  
  Purchase #7 $180.71   12.628%   $203.5301   $203.53   $203.55   $203.50  
  7 purchase totals = $1,095.29       $1,182.1803   $1,182.18   $1,182.20   $1,182.10