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 $59.44   10.292%   $65.5576   $65.56   $65.55   $65.60  
  Purchase #2 $180.43   3.394%   $186.5538   $186.55   $186.55   $186.60  
  Purchase #3 $157.57   3.405%   $162.9353   $162.94   $162.95   $162.90  
  Purchase #4 $86.39   10.379%   $95.3564   $95.36   $95.35   $95.40  
  Purchase #5 $246.80   12.138%   $276.7566   $276.76   $276.75   $276.80  
  Purchase #6 $14.33   6.688%   $15.2884   $15.29   $15.30   $15.30  
  Purchase #7 $228.47   11.705%   $255.2124   $255.21   $255.20   $255.20  
  7 purchase totals = $973.43       $1,057.6605   $1,057.67   $1,057.65   $1,057.80