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	$96.76	6.626%	$103.1713	$103.17	$103.15	$103.20
Purchase #2	$98.56	5.813%	$104.2893	$104.29	$104.30	$104.30
Purchase #3	$246.76	8.476%	$267.6754	$267.68	$267.70	$267.70
Purchase #4	$70.33	3.323%	$72.6671	$72.67	$72.65	$72.70
Purchase #5	$106.91	10.230%	$117.8469	$117.85	$117.85	$117.80
Purchase #6	$213.43	4.386%	$222.791	$222.79	$222.80	$222.80
Purchase #7	$158.46	5.573%	$167.291	$167.29	$167.30	$167.30
7 purchase totals =	$991.21		$1,055.7320	$1,055.74	$1,055.75	$1,055.80