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	$10.55	3.335%	$10.9018	$10.90	$10.90	$10.90
Purchase #2	$84.59	7.457%	$90.8979	$90.90	$90.90	$90.90
Purchase #3	$142.76	3.768%	$148.1392	$148.14	$148.15	$148.10
Purchase #4	$72.40	4.111%	$75.3764	$75.38	$75.40	$75.40
Purchase #5	$199.91	10.164%	$220.2289	$220.23	$220.25	$220.20
Purchase #6	$35.65	5.736%	$37.6949	$37.69	$37.70	$37.70
Purchase #7	$67.53	7.338%	$72.4854	$72.49	$72.50	$72.50
7 purchase totals =	$613.39		$655.7245	$655.73	$655.80	$655.70