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	$84.77	9.543%	$92.8596	$92.86	$92.85	$92.90
Purchase #2	$45.97	10.387%	$50.7449	$50.74	$50.75	$50.70
Purchase #3	$21.36	6.232%	$22.6912	$22.69	$22.70	$22.70
Purchase #4	$134.64	5.107%	$141.5161	$141.52	$141.50	$141.50
Purchase #5	$165.38	10.357%	$182.5084	$182.51	$182.50	$182.50
Purchase #6	$103.82	5.466%	$109.4948	$109.49	$109.50	$109.50
Purchase #7	$58.93	3.703%	$61.1122	$61.11	$61.10	$61.10
7 purchase totals =	$614.87		$660.9272	$660.92	$660.90	$660.90