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	$183.52	3.488%	$189.9212	$189.92	$189.90	$189.90
Purchase #2	$72.78	13.825%	$82.8418	$82.84	$82.85	$82.80
Purchase #3	$125.47	11.435%	$139.8175	$139.82	$139.80	$139.80
Purchase #4	$104.50	11.523%	$116.5415	$116.54	$116.55	$116.50
Purchase #5	$85.32	6.333%	$90.7233	$90.72	$90.70	$90.70
Purchase #6	$167.53	4.248%	$174.6467	$174.65	$174.65	$174.60
Purchase #7	$58.94	3.418%	$60.9546	$60.95	$60.95	$61.00
7 purchase totals =	$798.06		$855.4466	$855.44	$855.40	$855.30