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	$64.35	3.350%	$66.5057	$66.51	$66.50	$66.50
Purchase #2	$91.66	6.301%	$97.4355	$97.44	$97.45	$97.40
Purchase #3	$115.87	10.586%	$128.136	$128.14	$128.15	$128.10
Purchase #4	$167.33	13.478%	$189.8827	$189.88	$189.90	$189.90
Purchase #5	$54.37	10.192%	$59.9114	$59.91	$59.90	$59.90
Purchase #6	$71.59	10.402%	$79.0368	$79.04	$79.05	$79.00
Purchase #7	$49.59	7.677%	$53.397	$53.40	$53.40	$53.40
7 purchase totals =	$614.76		$674.3051	$674.32	$674.35	$674.20