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 $53.93   13.173%   $61.0342   $61.03   $61.05   $61.00  
  Purchase #2 $99.36   8.683%   $107.9874   $107.99   $108.00   $108.00  
  Purchase #3 $119.35   8.242%   $129.1868   $129.19   $129.20   $129.20  
  Purchase #4 $188.97   11.552%   $210.7998   $210.80   $210.80   $210.80  
  Purchase #5 $96.45   12.832%   $108.8265   $108.83   $108.85   $108.80  
  Purchase #6 $71.97   10.449%   $79.4901   $79.49   $79.50   $79.50  
  Purchase #7 $45.73   8.591%   $49.6587   $49.66   $49.65   $49.70  
  7 purchase totals = $675.76       $746.9835   $746.99   $747.05   $747.00