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	$143.41	3.817%	$148.884	$148.88	$148.90	$148.90
Purchase #2	$238.81	4.733%	$250.1129	$250.11	$250.10	$250.10
Purchase #3	$221.46	4.523%	$231.4766	$231.48	$231.50	$231.50
Purchase #4	$173.30	10.745%	$191.9211	$191.92	$191.90	$191.90
Purchase #5	$88.98	3.272%	$91.8914	$91.89	$91.90	$91.90
Purchase #6	$72.76	11.258%	$80.9513	$80.95	$80.95	$81.00
Purchase #7	$65.55	5.623%	$69.2359	$69.24	$69.25	$69.20
7 purchase totals =	$1,004.27		$1,064.4732	$1,064.47	$1,064.50	$1,064.50