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 $55.44   10.568%   $61.2989   $61.30   $61.30   $61.30  
  Purchase #2 $208.31   4.752%   $218.2089   $218.21   $218.20   $218.20  
  Purchase #3 $233.44   8.317%   $252.8552   $252.86   $252.85   $252.90  
  Purchase #4 $20.73   9.283%   $22.6544   $22.65   $22.65   $22.70  
  Purchase #5 $186.83   6.418%   $198.8207   $198.82   $198.80   $198.80  
  Purchase #6 $184.51   10.853%   $204.5349   $204.53   $204.55   $204.50  
  Purchase #7 $10.52   3.579%   $10.8965   $10.90   $10.90   $10.90  
  7 purchase totals = $899.78       $969.2695   $969.27   $969.25   $969.30