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	$228.56	3.364%	$236.2488	$236.25	$236.25	$236.20
Purchase #2	$174.43	9.411%	$190.8456	$190.85	$190.85	$190.80
Purchase #3	$218.95	5.723%	$231.4805	$231.48	$231.50	$231.50
Purchase #4	$223.39	5.227%	$235.0666	$235.07	$235.05	$235.10
Purchase #5	$71.52	6.817%	$76.3955	$76.40	$76.40	$76.40
Purchase #6	$241.27	11.314%	$268.5673	$268.57	$268.55	$268.60
Purchase #7	$85.93	4.614%	$89.8948	$89.89	$89.90	$89.90
7 purchase totals =	$1,244.05		$1,328.4991	$1,328.51	$1,328.50	$1,328.50