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	$80.82	13.511%	$91.7396	$91.74	$91.75	$91.70
Purchase #2	$110.56	9.239%	$120.7746	$120.77	$120.75	$120.80
Purchase #3	$151.96	9.753%	$166.7807	$166.78	$166.80	$166.80
Purchase #4	$166.36	11.572%	$185.6112	$185.61	$185.60	$185.60
Purchase #5	$136.96	12.614%	$154.2361	$154.24	$154.25	$154.20
Purchase #6	$36.84	10.729%	$40.7926	$40.79	$40.80	$40.80
Purchase #7	$72.72	13.473%	$82.5176	$82.52	$82.50	$82.50
7 purchase totals =	$756.22		$842.4524	$842.45	$842.45	$842.40