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	$213.72	7.347%	$229.422	$229.42	$229.40	$229.40
Purchase #2	$204.58	11.531%	$228.1701	$228.17	$228.15	$228.20
Purchase #3	$84.95	13.818%	$96.6884	$96.69	$96.70	$96.70
Purchase #4	$146.62	12.685%	$165.2187	$165.22	$165.20	$165.20
Purchase #5	$169.92	6.811%	$181.4933	$181.49	$181.50	$181.50
Purchase #6	$94.92	6.190%	$100.7955	$100.80	$100.80	$100.80
Purchase #7	$6.72	12.250%	$7.5432	$7.54	$7.55	$7.50
7 purchase totals =	$921.43		$1,009.3312	$1,009.33	$1,009.30	$1,009.30