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	$36.74	13.485%	$41.6944	$41.69	$41.70	$41.70
Purchase #2	$113.33	4.805%	$118.7755	$118.78	$118.80	$118.80
Purchase #3	$79.56	12.563%	$89.5551	$89.56	$89.55	$89.60
Purchase #4	$86.54	4.402%	$90.3495	$90.35	$90.35	$90.30
Purchase #5	$158.56	9.837%	$174.1575	$174.16	$174.15	$174.20
Purchase #6	$153.75	7.228%	$164.8631	$164.86	$164.85	$164.90
Purchase #7	$92.55	13.449%	$104.997	$105.00	$105.00	$105.00
7 purchase totals =	$721.03		$784.3921	$784.40	$784.40	$784.50