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	$250.47	10.792%	$277.5007	$277.50	$277.50	$277.50
Purchase #2	$173.93	3.729%	$180.4158	$180.42	$180.40	$180.40
Purchase #3	$94.35	11.453%	$105.1559	$105.16	$105.15	$105.20
Purchase #4	$44.92	12.637%	$50.5965	$50.60	$50.60	$50.60
Purchase #5	$140.57	7.409%	$150.9848	$150.98	$151.00	$151.00
Purchase #6	$160.95	8.695%	$174.9446	$174.94	$174.95	$174.90
Purchase #7	$120.29	3.849%	$124.92	$124.92	$124.90	$124.90
7 purchase totals =	$985.48		$1,064.5183	$1,064.52	$1,064.50	$1,064.50