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	$108.54	3.536%	$112.378	$112.38	$112.40	$112.40
Purchase #2	$155.91	7.290%	$167.2758	$167.28	$167.30	$167.30
Purchase #3	$166.86	9.264%	$182.3179	$182.32	$182.30	$182.30
Purchase #4	$82.30	5.418%	$86.759	$86.76	$86.75	$86.80
Purchase #5	$79.94	11.585%	$89.201	$89.20	$89.20	$89.20
Purchase #6	$5.31	6.231%	$5.6409	$5.64	$5.65	$5.60
Purchase #7	$90.25	10.852%	$100.0439	$100.04	$100.05	$100.00
7 purchase totals =	$689.11		$743.6165	$743.62	$743.65	$743.60