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	$229.51	10.368%	$253.3056	$253.31	$253.30	$253.30
Purchase #2	$159.40	12.585%	$179.4605	$179.46	$179.45	$179.50
Purchase #3	$140.97	7.478%	$151.5117	$151.51	$151.50	$151.50
Purchase #4	$125.79	3.532%	$130.2329	$130.23	$130.25	$130.20
Purchase #5	$126.74	11.655%	$141.5115	$141.51	$141.50	$141.50
Purchase #6	$77.40	3.547%	$80.1454	$80.15	$80.15	$80.10
Purchase #7	$119.84	3.788%	$124.3795	$124.38	$124.40	$124.40
7 purchase totals =	$979.65		$1,060.5471	$1,060.55	$1,060.55	$1,060.50