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	$37.51	4.403%	$39.1616	$39.16	$39.15	$39.20
Purchase #2	$175.88	4.821%	$184.3592	$184.36	$184.35	$184.40
Purchase #3	$167.52	6.396%	$178.2346	$178.23	$178.25	$178.20
Purchase #4	$98.41	11.462%	$109.6898	$109.69	$109.70	$109.70
Purchase #5	$155.66	11.343%	$173.3165	$173.32	$173.30	$173.30
Purchase #6	$201.44	10.751%	$223.0968	$223.10	$223.10	$223.10
Purchase #7	$95.68	9.113%	$104.3993	$104.40	$104.40	$104.40
7 purchase totals =	$932.10		$1,012.2578	$1,012.26	$1,012.25	$1,012.30