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	$89.36	11.750%	$99.8598	$99.86	$99.85	$99.90
Purchase #2	$94.74	13.487%	$107.5176	$107.52	$107.50	$107.50
Purchase #3	$243.50	3.452%	$251.9056	$251.91	$251.90	$251.90
Purchase #4	$234.84	8.326%	$254.3928	$254.39	$254.40	$254.40
Purchase #5	$206.98	6.553%	$220.5434	$220.54	$220.55	$220.50
Purchase #6	$59.68	13.250%	$67.5876	$67.59	$67.60	$67.60
Purchase #7	$192.73	12.432%	$216.6902	$216.69	$216.70	$216.70
7 purchase totals =	$1,121.83		$1,218.4970	$1,218.50	$1,218.50	$1,218.50