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	$161.52	3.151%	$166.6095	$166.61	$166.60	$166.60
Purchase #2	$225.67	7.573%	$242.76	$242.76	$242.75	$242.80
Purchase #3	$213.68	11.726%	$238.7361	$238.74	$238.75	$238.70
Purchase #4	$22.97	8.336%	$24.8848	$24.88	$24.90	$24.90
Purchase #5	$246.96	11.279%	$274.8146	$274.81	$274.80	$274.80
Purchase #6	$162.78	6.142%	$172.7779	$172.78	$172.80	$172.80
Purchase #7	$123.46	6.302%	$131.2404	$131.24	$131.25	$131.20
7 purchase totals =	$1,157.04		$1,251.8233	$1,251.82	$1,251.85	$1,251.80