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	$138.44	13.411%	$157.0062	$157.01	$157.00	$157.00
Purchase #2	$135.46	6.658%	$144.4789	$144.48	$144.50	$144.50
Purchase #3	$205.78	13.385%	$233.3237	$233.32	$233.30	$233.30
Purchase #4	$39.84	13.682%	$45.2909	$45.29	$45.30	$45.30
Purchase #5	$71.69	7.625%	$77.1564	$77.16	$77.15	$77.20
Purchase #6	$161.99	3.828%	$168.191	$168.19	$168.20	$168.20
Purchase #7	$78.52	13.170%	$88.8611	$88.86	$88.85	$88.90
7 purchase totals =	$831.72		$914.3082	$914.31	$914.30	$914.40