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	$113.74	4.290%	$118.6194	$118.62	$118.60	$118.60
Purchase #2	$215.47	10.524%	$238.1461	$238.15	$238.15	$238.10
Purchase #3	$30.30	6.120%	$32.1544	$32.15	$32.15	$32.20
Purchase #4	$83.61	8.525%	$90.7378	$90.74	$90.75	$90.70
Purchase #5	$26.72	13.398%	$30.2999	$30.30	$30.30	$30.30
Purchase #6	$109.62	10.300%	$120.9109	$120.91	$120.90	$120.90
Purchase #7	$243.86	10.605%	$269.7214	$269.72	$269.70	$269.70
7 purchase totals =	$823.32		$900.5899	$900.59	$900.55	$900.50