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	$100.78	6.697%	$107.5292	$107.53	$107.55	$107.50
Purchase #2	$147.78	10.267%	$162.9526	$162.95	$162.95	$163.00
Purchase #3	$88.40	3.187%	$91.2173	$91.22	$91.20	$91.20
Purchase #4	$126.64	7.837%	$136.5648	$136.56	$136.55	$136.60
Purchase #5	$104.61	5.673%	$110.5445	$110.54	$110.55	$110.50
Purchase #6	$63.39	13.821%	$72.1511	$72.15	$72.15	$72.20
Purchase #7	$99.35	12.523%	$111.7916	$111.79	$111.80	$111.80
7 purchase totals =	$730.95		$792.7511	$792.74	$792.75	$792.80