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	$31.37	13.168%	$35.5008	$35.50	$35.50	$35.50
Purchase #2	$150.62	6.824%	$160.8983	$160.90	$160.90	$160.90
Purchase #3	$165.50	3.190%	$170.7795	$170.78	$170.80	$170.80
Purchase #4	$150.57	12.506%	$169.4003	$169.40	$169.40	$169.40
Purchase #5	$54.80	8.672%	$59.5523	$59.55	$59.55	$59.60
Purchase #6	$65.87	12.579%	$74.1558	$74.16	$74.15	$74.20
Purchase #7	$57.46	9.520%	$62.9302	$62.93	$62.95	$62.90
7 purchase totals =	$676.19		$733.2172	$733.22	$733.25	$733.30