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 $233.47   13.715%   $265.4904   $265.49   $265.50   $265.50  
  Purchase #2 $52.95   7.329%   $56.8307   $56.83   $56.85   $56.80  
  Purchase #3 $160.79   9.322%   $175.7788   $175.78   $175.80   $175.80  
  Purchase #4 $22.49   7.253%   $24.1212   $24.12   $24.10   $24.10  
  Purchase #5 $215.48   5.468%   $227.2624   $227.26   $227.25   $227.30  
  Purchase #6 $211.44   6.808%   $225.8348   $225.83   $225.85   $225.80  
  Purchase #7 $43.68   10.725%   $48.3647   $48.36   $48.35   $48.40  
  7 purchase totals = $940.30       $1,023.6830   $1,023.67   $1,023.70   $1,023.70