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	$74.96	5.616%	$79.1698	$79.17	$79.15	$79.20
Purchase #2	$199.78	10.430%	$220.6171	$220.62	$220.60	$220.60
Purchase #3	$40.54	7.141%	$43.435	$43.44	$43.45	$43.40
Purchase #4	$64.66	12.873%	$72.9837	$72.98	$73.00	$73.00
Purchase #5	$158.55	6.755%	$169.2601	$169.26	$169.25	$169.30
Purchase #6	$90.63	6.799%	$96.7919	$96.79	$96.80	$96.80
Purchase #7	$82.74	9.159%	$90.3182	$90.32	$90.30	$90.30
7 purchase totals =	$711.86		$772.5758	$772.58	$772.55	$772.60