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	$10.98	10.404%	$12.1224	$12.12	$12.10	$12.10
Purchase #2	$119.52	9.216%	$130.535	$130.54	$130.55	$130.50
Purchase #3	$175.53	5.317%	$184.8629	$184.86	$184.85	$184.90
Purchase #4	$119.64	4.588%	$125.1291	$125.13	$125.15	$125.10
Purchase #5	$201.81	7.732%	$217.4139	$217.41	$217.40	$217.40
Purchase #6	$243.64	4.363%	$254.27	$254.27	$254.25	$254.30
Purchase #7	$127.80	11.375%	$142.3373	$142.34	$142.35	$142.30
7 purchase totals =	$998.92		$1,066.6706	$1,066.67	$1,066.65	$1,066.60