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	$35.69	4.146%	$37.1697	$37.17	$37.15	$37.20
Purchase #2	$34.48	11.412%	$38.4149	$38.41	$38.40	$38.40
Purchase #3	$190.32	10.760%	$210.7984	$210.80	$210.80	$210.80
Purchase #4	$158.61	4.869%	$166.3327	$166.33	$166.35	$166.30
Purchase #5	$176.34	8.425%	$191.1966	$191.20	$191.20	$191.20
Purchase #6	$18.52	11.489%	$20.6478	$20.65	$20.65	$20.60
Purchase #7	$166.84	10.655%	$184.6168	$184.62	$184.60	$184.60
7 purchase totals =	$780.80		$849.1769	$849.18	$849.15	$849.10