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	$53.62	11.695%	$59.8909	$59.89	$59.90	$59.90
Purchase #2	$90.43	13.348%	$102.5006	$102.50	$102.50	$102.50
Purchase #3	$181.85	6.614%	$193.8776	$193.88	$193.90	$193.90
Purchase #4	$57.75	11.145%	$64.1862	$64.19	$64.20	$64.20
Purchase #5	$160.82	10.782%	$178.1596	$178.16	$178.15	$178.20
Purchase #6	$211.54	11.263%	$235.3658	$235.37	$235.35	$235.40
Purchase #7	$146.40	13.270%	$165.8273	$165.83	$165.85	$165.80
7 purchase totals =	$902.41		$999.8080	$999.82	$999.85	$999.90