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	$148.64	9.142%	$162.2287	$162.23	$162.25	$162.20
Purchase #2	$207.77	5.375%	$218.9376	$218.94	$218.95	$218.90
Purchase #3	$12.72	12.242%	$14.2772	$14.28	$14.30	$14.30
Purchase #4	$50.79	9.686%	$55.7095	$55.71	$55.70	$55.70
Purchase #5	$81.59	9.590%	$89.4145	$89.41	$89.40	$89.40
Purchase #6	$234.44	3.798%	$243.344	$243.34	$243.35	$243.30
Purchase #7	$16.90	7.641%	$18.1913	$18.19	$18.20	$18.20
7 purchase totals =	$752.85		$802.1028	$802.10	$802.15	$802.00