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	$66.97	7.396%	$71.9231	$71.92	$71.90	$71.90
Purchase #2	$139.96	12.800%	$157.8749	$157.87	$157.85	$157.90
Purchase #3	$30.93	4.531%	$32.3314	$32.33	$32.35	$32.30
Purchase #4	$131.31	8.787%	$142.8482	$142.85	$142.85	$142.80
Purchase #5	$184.93	13.102%	$209.1595	$209.16	$209.15	$209.20
Purchase #6	$117.45	12.161%	$131.7331	$131.73	$131.75	$131.70
Purchase #7	$42.92	8.629%	$46.6236	$46.62	$46.60	$46.60
7 purchase totals =	$714.47		$792.4938	$792.48	$792.45	$792.40