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	$81.68	10.566%	$90.3103	$90.31	$90.30	$90.30
Purchase #2	$73.96	5.363%	$77.9265	$77.93	$77.95	$77.90
Purchase #3	$115.88	13.383%	$131.3882	$131.39	$131.40	$131.40
Purchase #4	$96.91	8.452%	$105.1008	$105.10	$105.10	$105.10
Purchase #5	$184.55	3.559%	$191.1181	$191.12	$191.10	$191.10
Purchase #6	$104.92	9.872%	$115.2777	$115.28	$115.30	$115.30
Purchase #7	$170.48	13.856%	$194.1017	$194.10	$194.10	$194.10
7 purchase totals =	$828.38		$905.2233	$905.23	$905.25	$905.20