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	$246.34	11.753%	$275.2923	$275.29	$275.30	$275.30
Purchase #2	$140.52	7.275%	$150.7428	$150.74	$150.75	$150.70
Purchase #3	$237.36	11.282%	$264.139	$264.14	$264.15	$264.10
Purchase #4	$195.59	10.379%	$215.8903	$215.89	$215.90	$215.90
Purchase #5	$125.67	3.539%	$130.1175	$130.12	$130.10	$130.10
Purchase #6	$98.60	5.472%	$103.9954	$104.00	$104.00	$104.00
Purchase #7	$166.88	7.487%	$179.3743	$179.37	$179.35	$179.40
7 purchase totals =	$1,210.96		$1,319.5516	$1,319.55	$1,319.55	$1,319.50