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	$82.97	7.410%	$89.1181	$89.12	$89.10	$89.10
Purchase #2	$109.78	11.836%	$122.7736	$122.77	$122.75	$122.80
Purchase #3	$124.68	7.419%	$133.93	$133.93	$133.95	$133.90
Purchase #4	$244.78	4.676%	$256.2259	$256.23	$256.25	$256.20
Purchase #5	$67.38	7.391%	$72.3601	$72.36	$72.35	$72.40
Purchase #6	$216.81	7.672%	$233.4437	$233.44	$233.45	$233.40
Purchase #7	$61.35	7.157%	$65.7408	$65.74	$65.75	$65.70
7 purchase totals =	$907.75		$973.5922	$973.59	$973.60	$973.50