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	$39.66	6.122%	$42.088	$42.09	$42.10	$42.10
Purchase #2	$22.71	6.856%	$24.267	$24.27	$24.25	$24.30
Purchase #3	$90.65	6.134%	$96.2105	$96.21	$96.20	$96.20
Purchase #4	$249.66	11.567%	$278.5382	$278.54	$278.55	$278.50
Purchase #5	$140.48	4.136%	$146.2903	$146.29	$146.30	$146.30
Purchase #6	$181.34	7.269%	$194.5216	$194.52	$194.50	$194.50
Purchase #7	$123.79	5.297%	$130.3472	$130.35	$130.35	$130.30
7 purchase totals =	$848.29		$912.2628	$912.27	$912.25	$912.20