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	$72.48	10.538%	$80.1179	$80.12	$80.10	$80.10
Purchase #2	$111.33	11.197%	$123.7956	$123.80	$123.80	$123.80
Purchase #3	$43.97	9.698%	$48.2342	$48.23	$48.25	$48.20
Purchase #4	$223.33	13.755%	$254.049	$254.05	$254.05	$254.00
Purchase #5	$38.40	12.471%	$43.1889	$43.19	$43.20	$43.20
Purchase #6	$187.40	10.590%	$207.2457	$207.25	$207.25	$207.20
Purchase #7	$238.98	11.412%	$266.2524	$266.25	$266.25	$266.30
7 purchase totals =	$915.89		$1,022.8837	$1,022.89	$1,022.90	$1,022.80