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 $223.91   7.633%   $241.0011   $241.00   $241.00   $241.00  
  Purchase #2 $66.67   4.411%   $69.6108   $69.61   $69.60   $69.60  
  Purchase #3 $61.39   7.764%   $66.1563   $66.16   $66.15   $66.20  
  Purchase #4 $45.74   9.458%   $50.0661   $50.07   $50.05   $50.10  
  Purchase #5 $245.83   8.249%   $266.1085   $266.11   $266.10   $266.10  
  Purchase #6 $111.64   9.680%   $122.4468   $122.45   $122.45   $122.40  
  Purchase #7 $83.85   5.718%   $88.6445   $88.64   $88.65   $88.60  
  7 purchase totals = $839.03       $904.0341   $904.04   $904.00   $904.00