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	$31.91	13.132%	$36.1004	$36.10	$36.10	$36.10
Purchase #2	$157.56	3.182%	$162.5736	$162.57	$162.55	$162.60
Purchase #3	$49.94	11.507%	$55.6866	$55.69	$55.70	$55.70
Purchase #4	$156.59	9.731%	$171.8278	$171.83	$171.85	$171.80
Purchase #5	$155.90	10.759%	$172.6733	$172.67	$172.65	$172.70
Purchase #6	$41.86	13.490%	$47.5069	$47.51	$47.50	$47.50
Purchase #7	$127.54	6.267%	$135.5329	$135.53	$135.55	$135.50
7 purchase totals =	$721.30		$781.9015	$781.90	$781.90	$781.90