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	$148.62	6.435%	$158.1837	$158.18	$158.20	$158.20
Purchase #2	$6.86	6.248%	$7.2886	$7.29	$7.30	$7.30
Purchase #3	$89.90	8.404%	$97.4552	$97.46	$97.45	$97.50
Purchase #4	$122.95	13.331%	$139.3405	$139.34	$139.35	$139.30
Purchase #5	$37.30	3.211%	$38.4977	$38.50	$38.50	$38.50
Purchase #6	$93.84	12.685%	$105.7436	$105.74	$105.75	$105.70
Purchase #7	$109.78	12.862%	$123.8999	$123.90	$123.90	$123.90
7 purchase totals =	$609.25		$670.4092	$670.41	$670.45	$670.40