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	$21.67	11.370%	$24.1339	$24.13	$24.15	$24.10
Purchase #2	$238.57	4.524%	$249.3629	$249.36	$249.35	$249.40
Purchase #3	$91.34	5.851%	$96.6843	$96.68	$96.70	$96.70
Purchase #4	$183.41	12.256%	$205.8887	$205.89	$205.90	$205.90
Purchase #5	$218.68	10.289%	$241.18	$241.18	$241.20	$241.20
Purchase #6	$185.91	12.272%	$208.7249	$208.72	$208.70	$208.70
Purchase #7	$64.36	11.700%	$71.8901	$71.89	$71.90	$71.90
7 purchase totals =	$1,003.94		$1,097.8648	$1,097.85	$1,097.90	$1,097.90