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	$70.28	11.656%	$78.4718	$78.47	$78.45	$78.50
Purchase #2	$50.72	10.586%	$56.0892	$56.09	$56.10	$56.10
Purchase #3	$229.69	8.603%	$249.4502	$249.45	$249.45	$249.50
Purchase #4	$87.33	13.559%	$99.1711	$99.17	$99.15	$99.20
Purchase #5	$203.67	8.180%	$220.3302	$220.33	$220.35	$220.30
Purchase #6	$73.42	11.460%	$81.8339	$81.83	$81.85	$81.80
Purchase #7	$93.84	13.865%	$106.8509	$106.85	$106.85	$106.90
7 purchase totals =	$808.95		$892.1973	$892.19	$892.20	$892.30