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	$151.30	13.173%	$171.2307	$171.23	$171.25	$171.20
Purchase #2	$78.80	13.314%	$89.2914	$89.29	$89.30	$89.30
Purchase #3	$171.97	10.107%	$189.351	$189.35	$189.35	$189.40
Purchase #4	$60.35	10.813%	$66.8756	$66.88	$66.90	$66.90
Purchase #5	$123.29	6.422%	$131.2077	$131.21	$131.20	$131.20
Purchase #6	$212.87	10.751%	$235.7557	$235.76	$235.75	$235.80
Purchase #7	$31.99	9.783%	$35.1196	$35.12	$35.10	$35.10
7 purchase totals =	$830.57		$918.8317	$918.84	$918.85	$918.90