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	$187.61	13.229%	$212.4289	$212.43	$212.45	$212.40
Purchase #2	$41.25	9.778%	$45.2834	$45.28	$45.30	$45.30
Purchase #3	$233.77	10.448%	$258.1943	$258.19	$258.20	$258.20
Purchase #4	$73.91	11.306%	$82.2663	$82.27	$82.25	$82.30
Purchase #5	$123.80	6.123%	$131.3803	$131.38	$131.40	$131.40
Purchase #6	$32.88	7.251%	$35.2641	$35.26	$35.25	$35.30
Purchase #7	$129.57	9.854%	$142.3378	$142.34	$142.35	$142.30
7 purchase totals =	$822.79		$907.1551	$907.15	$907.20	$907.20