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	$165.87	3.187%	$171.1563	$171.16	$171.15	$171.20
Purchase #2	$242.90	11.532%	$270.9112	$270.91	$270.90	$270.90
Purchase #3	$52.84	8.632%	$57.4011	$57.40	$57.40	$57.40
Purchase #4	$190.65	8.163%	$206.2128	$206.21	$206.20	$206.20
Purchase #5	$66.37	10.354%	$73.2419	$73.24	$73.25	$73.20
Purchase #6	$95.62	10.680%	$105.8322	$105.83	$105.85	$105.80
Purchase #7	$187.84	4.373%	$196.0542	$196.05	$196.05	$196.10
7 purchase totals =	$1,002.09		$1,080.8097	$1,080.80	$1,080.80	$1,080.80