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	$139.91	12.296%	$157.1133	$157.11	$157.10	$157.10
Purchase #2	$145.31	8.254%	$157.3039	$157.30	$157.30	$157.30
Purchase #3	$174.50	12.595%	$196.4783	$196.48	$196.50	$196.50
Purchase #4	$114.89	3.803%	$119.2593	$119.26	$119.25	$119.30
Purchase #5	$105.79	3.479%	$109.4704	$109.47	$109.45	$109.50
Purchase #6	$44.39	11.599%	$49.5388	$49.54	$49.55	$49.50
Purchase #7	$231.76	10.561%	$256.2362	$256.24	$256.25	$256.20
7 purchase totals =	$956.55		$1,045.4002	$1,045.40	$1,045.40	$1,045.40