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	$148.92	7.131%	$159.5395	$159.54	$159.55	$159.50
Purchase #2	$84.46	5.565%	$89.1602	$89.16	$89.15	$89.20
Purchase #3	$189.87	10.124%	$209.0924	$209.09	$209.10	$209.10
Purchase #4	$50.74	4.206%	$52.8741	$52.87	$52.85	$52.90
Purchase #5	$75.28	6.696%	$80.3207	$80.32	$80.30	$80.30
Purchase #6	$230.87	10.196%	$254.4095	$254.41	$254.40	$254.40
Purchase #7	$145.98	12.265%	$163.8844	$163.88	$163.90	$163.90
7 purchase totals =	$926.12		$1,009.2808	$1,009.27	$1,009.25	$1,009.30