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	$54.56	5.458%	$57.5379	$57.54	$57.55	$57.50
Purchase #2	$148.59	13.459%	$168.5887	$168.59	$168.60	$168.60
Purchase #3	$159.38	8.436%	$172.8253	$172.83	$172.85	$172.80
Purchase #4	$131.36	12.607%	$147.9206	$147.92	$147.90	$147.90
Purchase #5	$98.95	5.369%	$104.2626	$104.26	$104.25	$104.30
Purchase #6	$9.56	4.367%	$9.9775	$9.98	$10.00	$10.00
Purchase #7	$223.55	13.369%	$253.4364	$253.44	$253.45	$253.40
7 purchase totals =	$825.95		$914.5490	$914.56	$914.60	$914.50