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	$94.76	10.368%	$104.5847	$104.58	$104.60	$104.60
Purchase #2	$228.92	3.274%	$236.4148	$236.41	$236.40	$236.40
Purchase #3	$188.86	9.725%	$207.2266	$207.23	$207.25	$207.20
Purchase #4	$186.25	7.792%	$200.7626	$200.76	$200.75	$200.80
Purchase #5	$167.85	6.780%	$179.2302	$179.23	$179.25	$179.20
Purchase #6	$83.74	7.847%	$90.3111	$90.31	$90.30	$90.30
Purchase #7	$61.70	12.380%	$69.3385	$69.34	$69.35	$69.30
7 purchase totals =	$1,012.08		$1,087.8685	$1,087.86	$1,087.90	$1,087.80