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	$91.44	10.434%	$100.9808	$100.98	$101.00	$101.00
Purchase #2	$137.83	4.615%	$144.1909	$144.19	$144.20	$144.20
Purchase #3	$66.82	5.859%	$70.735	$70.74	$70.75	$70.70
Purchase #4	$128.41	12.543%	$144.5165	$144.52	$144.50	$144.50
Purchase #5	$46.31	9.869%	$50.8803	$50.88	$50.90	$50.90
Purchase #6	$42.72	11.803%	$47.7622	$47.76	$47.75	$47.80
Purchase #7	$96.78	7.372%	$103.9146	$103.91	$103.90	$103.90
7 purchase totals =	$610.31		$662.9803	$662.98	$663.00	$663.00