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	$36.33	13.328%	$41.1721	$41.17	$41.15	$41.20
Purchase #2	$182.28	3.282%	$188.2624	$188.26	$188.25	$188.30
Purchase #3	$172.48	5.820%	$182.5183	$182.52	$182.50	$182.50
Purchase #4	$27.69	13.425%	$31.4074	$31.41	$31.40	$31.40
Purchase #5	$97.88	6.658%	$104.3969	$104.40	$104.40	$104.40
Purchase #6	$34.96	8.132%	$37.8029	$37.80	$37.80	$37.80
Purchase #7	$214.85	13.820%	$244.5423	$244.54	$244.55	$244.50
7 purchase totals =	$766.47		$830.1023	$830.10	$830.05	$830.10