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	$95.69	4.617%	$100.108	$100.11	$100.10	$100.10
Purchase #2	$46.95	13.736%	$53.3991	$53.40	$53.40	$53.40
Purchase #3	$117.73	10.143%	$129.6714	$129.67	$129.65	$129.70
Purchase #4	$31.78	10.238%	$35.0336	$35.03	$35.05	$35.00
Purchase #5	$36.80	9.538%	$40.31	$40.31	$40.30	$40.30
Purchase #6	$98.26	11.370%	$109.4322	$109.43	$109.45	$109.40
Purchase #7	$5.31	3.162%	$5.4779	$5.48	$5.50	$5.50
7 purchase totals =	$432.52		$473.4322	$473.43	$473.45	$473.40