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	$169.69	6.187%	$180.1887	$180.19	$180.20	$180.20
Purchase #2	$84.44	7.595%	$90.8532	$90.85	$90.85	$90.90
Purchase #3	$72.54	8.839%	$78.9518	$78.95	$78.95	$79.00
Purchase #4	$64.32	4.609%	$67.2845	$67.28	$67.30	$67.30
Purchase #5	$91.81	13.733%	$104.4183	$104.42	$104.40	$104.40
Purchase #6	$131.76	5.599%	$139.1372	$139.14	$139.15	$139.10
Purchase #7	$191.70	10.512%	$211.8515	$211.85	$211.85	$211.90
7 purchase totals =	$806.26		$872.6852	$872.68	$872.70	$872.80