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	$240.71	12.633%	$271.1189	$271.12	$271.10	$271.10
Purchase #2	$103.33	9.727%	$113.3809	$113.38	$113.40	$113.40
Purchase #3	$25.74	11.792%	$28.7753	$28.78	$28.80	$28.80
Purchase #4	$121.32	13.663%	$137.896	$137.90	$137.90	$137.90
Purchase #5	$64.68	10.228%	$71.2955	$71.30	$71.30	$71.30
Purchase #6	$164.97	8.605%	$179.1657	$179.17	$179.15	$179.20
Purchase #7	$191.78	4.628%	$200.6556	$200.66	$200.65	$200.70
7 purchase totals =	$912.53		$1,002.2879	$1,002.31	$1,002.30	$1,002.40