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	$79.53	4.759%	$83.3148	$83.31	$83.30	$83.30
Purchase #2	$97.91	6.363%	$104.14	$104.14	$104.15	$104.10
Purchase #3	$61.33	4.700%	$64.2125	$64.21	$64.20	$64.20
Purchase #4	$130.93	7.836%	$141.1897	$141.19	$141.20	$141.20
Purchase #5	$116.90	13.394%	$132.5576	$132.56	$132.55	$132.60
Purchase #6	$22.93	11.404%	$25.5449	$25.54	$25.55	$25.50
Purchase #7	$80.70	12.276%	$90.6067	$90.61	$90.60	$90.60
7 purchase totals =	$590.23		$641.5662	$641.56	$641.55	$641.50