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	$168.33	6.687%	$179.5862	$179.59	$179.60	$179.60
Purchase #2	$136.37	8.219%	$147.5783	$147.58	$147.60	$147.60
Purchase #3	$84.70	9.527%	$92.7694	$92.77	$92.75	$92.80
Purchase #4	$55.54	10.253%	$61.2345	$61.23	$61.25	$61.20
Purchase #5	$92.66	6.858%	$99.0146	$99.01	$99.00	$99.00
Purchase #6	$169.98	11.395%	$189.3492	$189.35	$189.35	$189.30
Purchase #7	$183.69	8.629%	$199.5406	$199.54	$199.55	$199.50
7 purchase totals =	$891.27		$969.0728	$969.07	$969.10	$969.00