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 $216.91   13.431%   $246.0432   $246.04   $246.05   $246.00  
  Purchase #2 $131.67   11.587%   $146.9266   $146.93   $146.95   $146.90  
  Purchase #3 $160.95   3.196%   $166.094   $166.09   $166.10   $166.10  
  Purchase #4 $112.28   12.448%   $126.2566   $126.26   $126.25   $126.30  
  Purchase #5 $117.28   9.188%   $128.0557   $128.06   $128.05   $128.10  
  Purchase #6 $219.93   4.301%   $229.3892   $229.39   $229.40   $229.40  
  Purchase #7 $50.60   5.438%   $53.3516   $53.35   $53.35   $53.40  
  7 purchase totals = $1,009.62       $1,096.1169   $1,096.12   $1,096.15   $1,096.20