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	$41.77	3.485%	$43.2257	$43.23	$43.25	$43.20
Purchase #2	$152.58	11.404%	$169.9802	$169.98	$170.00	$170.00
Purchase #3	$30.98	6.602%	$33.0253	$33.03	$33.05	$33.00
Purchase #4	$80.48	4.141%	$83.8127	$83.81	$83.80	$83.80
Purchase #5	$204.84	11.534%	$228.4662	$228.47	$228.45	$228.50
Purchase #6	$247.86	11.304%	$275.8781	$275.88	$275.90	$275.90
Purchase #7	$105.38	9.474%	$115.3637	$115.36	$115.35	$115.40
7 purchase totals =	$863.89		$949.7519	$949.76	$949.80	$949.80