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	$245.51	12.757%	$276.8297	$276.83	$276.85	$276.80
Purchase #2	$213.30	12.653%	$240.2888	$240.29	$240.30	$240.30
Purchase #3	$140.31	3.427%	$145.1184	$145.12	$145.10	$145.10
Purchase #4	$146.74	3.465%	$151.8245	$151.82	$151.80	$151.80
Purchase #5	$218.47	11.650%	$243.9218	$243.92	$243.90	$243.90
Purchase #6	$147.77	13.647%	$167.9362	$167.94	$167.95	$167.90
Purchase #7	$41.92	9.128%	$45.7465	$45.75	$45.75	$45.70
7 purchase totals =	$1,154.02		$1,271.6659	$1,271.67	$1,271.65	$1,271.50