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	$186.45	6.662%	$198.8713	$198.87	$198.85	$198.90
Purchase #2	$175.82	9.819%	$193.0838	$193.08	$193.10	$193.10
Purchase #3	$146.74	12.340%	$164.8477	$164.85	$164.85	$164.80
Purchase #4	$80.32	12.450%	$90.3198	$90.32	$90.30	$90.30
Purchase #5	$218.72	11.167%	$243.1445	$243.14	$243.15	$243.10
Purchase #6	$58.78	13.370%	$66.6389	$66.64	$66.65	$66.60
Purchase #7	$75.25	13.124%	$85.1258	$85.13	$85.15	$85.10
7 purchase totals =	$942.08		$1,042.0318	$1,042.03	$1,042.05	$1,041.90