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	$190.58	11.858%	$213.179	$213.18	$213.20	$213.20
Purchase #2	$36.71	7.375%	$39.4174	$39.42	$39.40	$39.40
Purchase #3	$137.82	5.801%	$145.8149	$145.81	$145.80	$145.80
Purchase #4	$66.89	7.853%	$72.1429	$72.14	$72.15	$72.10
Purchase #5	$59.67	13.809%	$67.9098	$67.91	$67.90	$67.90
Purchase #6	$20.56	8.268%	$22.2599	$22.26	$22.25	$22.30
Purchase #7	$7.94	8.820%	$8.6403	$8.64	$8.65	$8.60
7 purchase totals =	$520.17		$569.3642	$569.36	$569.35	$569.30