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	$80.50	11.111%	$89.4444	$89.44	$89.45	$89.40
Purchase #2	$84.76	7.726%	$91.3086	$91.31	$91.30	$91.30
Purchase #3	$135.99	13.211%	$153.9556	$153.96	$153.95	$154.00
Purchase #4	$118.58	4.680%	$124.1295	$124.13	$124.15	$124.10
Purchase #5	$40.36	6.800%	$43.1045	$43.10	$43.10	$43.10
Purchase #6	$172.80	4.479%	$180.5397	$180.54	$180.55	$180.50
Purchase #7	$148.56	12.476%	$167.0943	$167.09	$167.10	$167.10
7 purchase totals =	$781.55		$849.5766	$849.57	$849.60	$849.50