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	$6.57	10.589%	$7.2657	$7.27	$7.25	$7.30
Purchase #2	$65.27	9.242%	$71.3023	$71.30	$71.30	$71.30
Purchase #3	$238.84	4.110%	$248.6563	$248.66	$248.65	$248.70
Purchase #4	$218.26	9.254%	$238.4578	$238.46	$238.45	$238.50
Purchase #5	$123.42	11.244%	$137.2973	$137.30	$137.30	$137.30
Purchase #6	$184.95	7.235%	$198.3311	$198.33	$198.35	$198.30
Purchase #7	$104.99	11.369%	$116.9263	$116.93	$116.95	$116.90
7 purchase totals =	$942.30		$1,018.2368	$1,018.25	$1,018.25	$1,018.30