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	$84.78	5.394%	$89.353	$89.35	$89.35	$89.40
Purchase #2	$241.72	10.787%	$267.7943	$267.79	$267.80	$267.80
Purchase #3	$38.84	13.222%	$43.9754	$43.98	$44.00	$44.00
Purchase #4	$96.31	4.712%	$100.8481	$100.85	$100.85	$100.80
Purchase #5	$118.87	10.323%	$131.141	$131.14	$131.15	$131.10
Purchase #6	$125.69	11.814%	$140.539	$140.54	$140.55	$140.50
Purchase #7	$106.41	13.369%	$120.636	$120.64	$120.65	$120.60
7 purchase totals =	$812.62		$894.2868	$894.29	$894.35	$894.20