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	$83.30	8.481%	$90.3647	$90.36	$90.35	$90.40
Purchase #2	$37.48	6.429%	$39.8896	$39.89	$39.90	$39.90
Purchase #3	$122.31	3.154%	$126.1677	$126.17	$126.15	$126.20
Purchase #4	$26.71	5.266%	$28.1165	$28.12	$28.10	$28.10
Purchase #5	$26.85	9.443%	$29.3854	$29.39	$29.40	$29.40
Purchase #6	$38.52	7.458%	$41.3928	$41.39	$41.40	$41.40
Purchase #7	$40.25	5.608%	$42.5072	$42.51	$42.50	$42.50
7 purchase totals =	$375.42		$397.8239	$397.83	$397.80	$397.90