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	$99.25	8.107%	$107.2962	$107.30	$107.30	$107.30
Purchase #2	$92.62	12.136%	$103.8604	$103.86	$103.85	$103.90
Purchase #3	$240.34	13.649%	$273.144	$273.14	$273.15	$273.10
Purchase #4	$35.33	6.136%	$37.4978	$37.50	$37.50	$37.50
Purchase #5	$99.88	6.123%	$105.9957	$106.00	$106.00	$106.00
Purchase #6	$107.46	12.523%	$120.9172	$120.92	$120.90	$120.90
Purchase #7	$64.33	11.831%	$71.9409	$71.94	$71.95	$71.90
7 purchase totals =	$739.21		$820.6522	$820.66	$820.65	$820.60