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	$90.90	12.112%	$101.9098	$101.91	$101.90	$101.90
Purchase #2	$134.33	11.762%	$150.1299	$150.13	$150.15	$150.10
Purchase #3	$204.41	12.421%	$229.7998	$229.80	$229.80	$229.80
Purchase #4	$183.28	8.757%	$199.3298	$199.33	$199.35	$199.30
Purchase #5	$166.92	10.757%	$184.8756	$184.88	$184.90	$184.90
Purchase #6	$42.60	10.454%	$47.0534	$47.05	$47.05	$47.10
Purchase #7	$152.85	8.186%	$165.3623	$165.36	$165.35	$165.40
7 purchase totals =	$975.29		$1,078.4606	$1,078.46	$1,078.50	$1,078.50