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	$134.72	8.771%	$146.5363	$146.54	$146.55	$146.50
Purchase #2	$187.72	12.502%	$211.1888	$211.19	$211.20	$211.20
Purchase #3	$156.48	8.351%	$169.5476	$169.55	$169.55	$169.50
Purchase #4	$207.54	9.536%	$227.331	$227.33	$227.35	$227.30
Purchase #5	$140.56	8.575%	$152.613	$152.61	$152.60	$152.60
Purchase #6	$182.94	7.393%	$196.4648	$196.46	$196.45	$196.50
Purchase #7	$223.99	6.363%	$238.2425	$238.24	$238.25	$238.20
7 purchase totals =	$1,233.95		$1,341.9240	$1,341.92	$1,341.95	$1,341.80