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	$203.65	4.170%	$212.1422	$212.14	$212.15	$212.10
Purchase #2	$201.86	13.190%	$228.4853	$228.49	$228.50	$228.50
Purchase #3	$222.69	5.243%	$234.3656	$234.37	$234.35	$234.40
Purchase #4	$219.60	8.319%	$237.8685	$237.87	$237.85	$237.90
Purchase #5	$19.45	8.646%	$21.1316	$21.13	$21.15	$21.10
Purchase #6	$96.49	13.331%	$109.3531	$109.35	$109.35	$109.40
Purchase #7	$53.46	11.796%	$59.7661	$59.77	$59.75	$59.80
7 purchase totals =	$1,017.20		$1,103.1124	$1,103.12	$1,103.10	$1,103.20