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	$207.37	12.148%	$232.5613	$232.56	$232.55	$232.60
Purchase #2	$129.88	4.259%	$135.4116	$135.41	$135.40	$135.40
Purchase #3	$29.53	9.206%	$32.2485	$32.25	$32.25	$32.20
Purchase #4	$25.96	11.110%	$28.8442	$28.84	$28.85	$28.80
Purchase #5	$196.28	13.162%	$222.1144	$222.11	$222.10	$222.10
Purchase #6	$101.55	10.184%	$111.8919	$111.89	$111.90	$111.90
Purchase #7	$96.25	5.264%	$101.3166	$101.32	$101.30	$101.30
7 purchase totals =	$786.82		$864.3885	$864.38	$864.35	$864.30