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	$44.79	10.759%	$49.609	$49.61	$49.60	$49.60
Purchase #2	$124.93	8.409%	$135.4354	$135.44	$135.45	$135.40
Purchase #3	$85.80	4.336%	$89.5203	$89.52	$89.50	$89.50
Purchase #4	$87.29	13.546%	$99.1143	$99.11	$99.10	$99.10
Purchase #5	$56.94	4.308%	$59.393	$59.39	$59.40	$59.40
Purchase #6	$130.40	6.696%	$139.1316	$139.13	$139.15	$139.10
Purchase #7	$105.71	9.216%	$115.4522	$115.45	$115.45	$115.50
7 purchase totals =	$635.86		$687.6558	$687.65	$687.65	$687.60