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	$55.31	3.613%	$57.3084	$57.31	$57.30	$57.30
Purchase #2	$157.34	4.775%	$164.853	$164.85	$164.85	$164.90
Purchase #3	$89.32	3.215%	$92.1916	$92.19	$92.20	$92.20
Purchase #4	$181.95	4.779%	$190.6454	$190.65	$190.65	$190.60
Purchase #5	$71.99	8.819%	$78.3388	$78.34	$78.35	$78.30
Purchase #6	$110.51	7.720%	$119.0414	$119.04	$119.05	$119.00
Purchase #7	$31.79	5.133%	$33.4218	$33.42	$33.40	$33.40
7 purchase totals =	$698.21		$735.8004	$735.80	$735.80	$735.70