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	$87.90	13.637%	$99.8869	$99.89	$99.90	$99.90
Purchase #2	$121.97	5.172%	$128.2783	$128.28	$128.30	$128.30
Purchase #3	$90.30	5.556%	$95.3171	$95.32	$95.30	$95.30
Purchase #4	$178.28	8.486%	$193.4088	$193.41	$193.40	$193.40
Purchase #5	$170.97	4.343%	$178.3952	$178.40	$178.40	$178.40
Purchase #6	$170.71	9.388%	$186.7363	$186.74	$186.75	$186.70
Purchase #7	$99.73	6.172%	$105.8853	$105.89	$105.90	$105.90
7 purchase totals =	$919.86		$987.9079	$987.93	$987.95	$987.90