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	$11.31	11.489%	$12.6094	$12.61	$12.60	$12.60
Purchase #2	$243.29	7.369%	$261.218	$261.22	$261.20	$261.20
Purchase #3	$173.70	13.342%	$196.8751	$196.88	$196.90	$196.90
Purchase #4	$88.54	5.197%	$93.1414	$93.14	$93.15	$93.10
Purchase #5	$30.28	10.114%	$33.3425	$33.34	$33.35	$33.30
Purchase #6	$220.38	4.426%	$230.134	$230.13	$230.15	$230.10
Purchase #7	$89.51	7.835%	$96.5231	$96.52	$96.50	$96.50
7 purchase totals =	$857.01		$923.8435	$923.84	$923.85	$923.70