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	$152.61	5.730%	$161.3546	$161.35	$161.35	$161.40
Purchase #2	$116.70	11.781%	$130.4484	$130.45	$130.45	$130.40
Purchase #3	$151.79	13.469%	$172.2346	$172.23	$172.25	$172.20
Purchase #4	$135.64	9.428%	$148.4281	$148.43	$148.45	$148.40
Purchase #5	$40.88	3.854%	$42.4555	$42.46	$42.45	$42.50
Purchase #6	$115.26	7.488%	$123.8907	$123.89	$123.90	$123.90
Purchase #7	$71.45	8.791%	$77.7312	$77.73	$77.75	$77.70
7 purchase totals =	$784.33		$856.5431	$856.54	$856.60	$856.50