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 $91.96   10.170%   $101.3123   $101.31   $101.30   $101.30  
  Purchase #2 $18.44   11.436%   $20.5488   $20.55   $20.55   $20.50  
  Purchase #3 $115.81   3.837%   $120.2536   $120.25   $120.25   $120.30  
  Purchase #4 $24.84   6.705%   $26.5055   $26.51   $26.50   $26.50  
  Purchase #5 $76.34   3.873%   $79.2966   $79.30   $79.30   $79.30  
  Purchase #6 $175.26   10.180%   $193.1015   $193.10   $193.10   $193.10  
  Purchase #7 $205.81   7.448%   $221.1387   $221.14   $221.15   $221.10  
  7 purchase totals = $708.46       $762.1570   $762.16   $762.15   $762.10