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	$35.67	6.240%	$37.8958	$37.90	$37.90	$37.90
Purchase #2	$138.25	8.346%	$149.7883	$149.79	$149.80	$149.80
Purchase #3	$163.38	11.277%	$181.8044	$181.80	$181.80	$181.80
Purchase #4	$150.86	10.846%	$167.2223	$167.22	$167.20	$167.20
Purchase #5	$83.51	11.339%	$92.9792	$92.98	$93.00	$93.00
Purchase #6	$127.35	10.799%	$141.1025	$141.10	$141.10	$141.10
Purchase #7	$155.54	7.713%	$167.5368	$167.54	$167.55	$167.50
7 purchase totals =	$854.56		$938.3293	$938.33	$938.35	$938.30