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	$247.33	11.551%	$275.8991	$275.90	$275.90	$275.90
Purchase #2	$152.54	4.623%	$159.5919	$159.59	$159.60	$159.60
Purchase #3	$25.34	7.107%	$27.1409	$27.14	$27.15	$27.10
Purchase #4	$163.94	10.238%	$180.7242	$180.72	$180.70	$180.70
Purchase #5	$205.92	12.572%	$231.8083	$231.81	$231.80	$231.80
Purchase #6	$73.73	3.426%	$76.256	$76.26	$76.25	$76.30
Purchase #7	$127.85	6.782%	$136.5208	$136.52	$136.50	$136.50
7 purchase totals =	$996.65		$1,087.9412	$1,087.94	$1,087.90	$1,087.90