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	$155.54	6.360%	$165.4323	$165.43	$165.45	$165.40
Purchase #2	$142.64	3.445%	$147.5539	$147.55	$147.55	$147.60
Purchase #3	$41.26	10.560%	$45.6171	$45.62	$45.60	$45.60
Purchase #4	$137.46	10.221%	$151.5098	$151.51	$151.50	$151.50
Purchase #5	$220.68	12.323%	$247.8744	$247.87	$247.85	$247.90
Purchase #6	$53.88	4.752%	$56.4404	$56.44	$56.45	$56.40
Purchase #7	$130.73	6.711%	$139.5033	$139.50	$139.50	$139.50
7 purchase totals =	$882.19		$953.9312	$953.92	$953.90	$953.90