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	$31.26	9.810%	$34.3266	$34.33	$34.35	$34.30
Purchase #2	$83.72	8.459%	$90.8019	$90.80	$90.80	$90.80
Purchase #3	$244.54	12.669%	$275.5208	$275.52	$275.50	$275.50
Purchase #4	$222.31	11.270%	$247.3643	$247.36	$247.35	$247.40
Purchase #5	$162.39	4.419%	$169.566	$169.57	$169.55	$169.60
Purchase #6	$209.72	8.287%	$227.0995	$227.10	$227.10	$227.10
Purchase #7	$213.66	6.255%	$227.0244	$227.02	$227.00	$227.00
7 purchase totals =	$1,167.60		$1,271.7035	$1,271.70	$1,271.65	$1,271.70