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	$96.61	6.498%	$102.8877	$102.89	$102.90	$102.90
Purchase #2	$160.64	12.603%	$180.8855	$180.89	$180.90	$180.90
Purchase #3	$60.97	6.339%	$64.8349	$64.83	$64.85	$64.80
Purchase #4	$246.68	3.167%	$254.4924	$254.49	$254.50	$254.50
Purchase #5	$74.41	10.352%	$82.1129	$82.11	$82.10	$82.10
Purchase #6	$231.63	4.111%	$241.1523	$241.15	$241.15	$241.20
Purchase #7	$245.45	11.198%	$272.9355	$272.94	$272.95	$272.90
7 purchase totals =	$1,116.39		$1,199.3012	$1,199.30	$1,199.35	$1,199.30