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	$96.98	3.868%	$100.7312	$100.73	$100.75	$100.70
Purchase #2	$32.59	3.121%	$33.6071	$33.61	$33.60	$33.60
Purchase #3	$46.57	9.316%	$50.9085	$50.91	$50.90	$50.90
Purchase #4	$156.42	3.772%	$162.3202	$162.32	$162.30	$162.30
Purchase #5	$114.86	8.506%	$124.63	$124.63	$124.65	$124.60
Purchase #6	$228.71	12.144%	$256.4845	$256.48	$256.50	$256.50
Purchase #7	$71.93	13.418%	$81.5816	$81.58	$81.60	$81.60
7 purchase totals =	$748.06		$810.2631	$810.26	$810.30	$810.20