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	$136.52	4.539%	$142.7166	$142.72	$142.70	$142.70
Purchase #2	$203.84	11.561%	$227.4059	$227.41	$227.40	$227.40
Purchase #3	$91.29	11.810%	$102.0713	$102.07	$102.05	$102.10
Purchase #4	$93.88	4.874%	$98.4557	$98.46	$98.45	$98.50
Purchase #5	$222.91	9.183%	$243.3798	$243.38	$243.40	$243.40
Purchase #6	$62.64	10.127%	$68.9836	$68.98	$69.00	$69.00
Purchase #7	$152.82	4.585%	$159.8268	$159.83	$159.85	$159.80
7 purchase totals =	$963.90		$1,042.8397	$1,042.85	$1,042.85	$1,042.90