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	$141.80	6.650%	$151.2297	$151.23	$151.25	$151.20
Purchase #2	$156.45	10.613%	$173.054	$173.05	$173.05	$173.10
Purchase #3	$93.76	12.872%	$105.8288	$105.83	$105.85	$105.80
Purchase #4	$204.89	4.275%	$213.649	$213.65	$213.65	$213.60
Purchase #5	$183.98	13.660%	$209.1117	$209.11	$209.10	$209.10
Purchase #6	$62.92	6.686%	$67.1268	$67.13	$67.15	$67.10
Purchase #7	$75.25	4.755%	$78.8281	$78.83	$78.85	$78.80
7 purchase totals =	$919.05		$998.8281	$998.83	$998.90	$998.70