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	$39.64	6.565%	$42.2424	$42.24	$42.25	$42.20
Purchase #2	$149.40	12.411%	$167.942	$167.94	$167.95	$167.90
Purchase #3	$205.33	5.109%	$215.8203	$215.82	$215.80	$215.80
Purchase #4	$117.93	11.867%	$131.9248	$131.92	$131.90	$131.90
Purchase #5	$211.68	4.219%	$220.6108	$220.61	$220.60	$220.60
Purchase #6	$223.29	11.736%	$249.4953	$249.50	$249.50	$249.50
Purchase #7	$212.77	8.796%	$231.4852	$231.49	$231.50	$231.50
7 purchase totals =	$1,160.04		$1,259.5208	$1,259.52	$1,259.50	$1,259.40