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	$164.87	11.843%	$184.3956	$184.40	$184.40	$184.40
Purchase #2	$43.76	8.568%	$47.5094	$47.51	$47.50	$47.50
Purchase #3	$185.93	12.206%	$208.6246	$208.62	$208.60	$208.60
Purchase #4	$147.53	3.393%	$152.5357	$152.54	$152.55	$152.50
Purchase #5	$144.82	5.194%	$152.342	$152.34	$152.35	$152.30
Purchase #6	$245.32	9.326%	$268.1985	$268.20	$268.20	$268.20
Purchase #7	$128.93	6.823%	$137.7269	$137.73	$137.75	$137.70
7 purchase totals =	$1,061.16		$1,151.3327	$1,151.34	$1,151.35	$1,151.20