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	$149.47	8.596%	$162.3184	$162.32	$162.30	$162.30
Purchase #2	$84.64	11.375%	$94.2678	$94.27	$94.25	$94.30
Purchase #3	$54.70	9.298%	$59.786	$59.79	$59.80	$59.80
Purchase #4	$188.32	4.160%	$196.1541	$196.15	$196.15	$196.20
Purchase #5	$38.53	6.650%	$41.0922	$41.09	$41.10	$41.10
Purchase #6	$152.94	12.423%	$171.9397	$171.94	$171.95	$171.90
Purchase #7	$235.52	3.736%	$244.319	$244.32	$244.30	$244.30
7 purchase totals =	$904.12		$969.8772	$969.88	$969.85	$969.90