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 $185.76   8.836%   $202.1738   $202.17   $202.15   $202.20  
  Purchase #2 $119.91   12.269%   $134.6218   $134.62   $134.60   $134.60  
  Purchase #3 $63.41   8.587%   $68.855   $68.86   $68.85   $68.90  
  Purchase #4 $27.75   12.751%   $31.2884   $31.29   $31.30   $31.30  
  Purchase #5 $243.54   3.244%   $251.4404   $251.44   $251.45   $251.40  
  Purchase #6 $51.92   11.413%   $57.8456   $57.85   $57.85   $57.80  
  Purchase #7 $170.25   4.637%   $178.1445   $178.14   $178.15   $178.10  
  7 purchase totals = $862.54       $924.3695   $924.37   $924.35   $924.30