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	$59.48	9.360%	$65.0473	$65.05	$65.05	$65.00
Purchase #2	$148.93	6.846%	$159.1257	$159.13	$159.15	$159.10
Purchase #3	$148.37	11.142%	$164.9014	$164.90	$164.90	$164.90
Purchase #4	$39.80	5.209%	$41.8732	$41.87	$41.85	$41.90
Purchase #5	$75.49	7.822%	$81.3948	$81.39	$81.40	$81.40
Purchase #6	$100.78	4.676%	$105.4925	$105.49	$105.50	$105.50
Purchase #7	$53.84	4.129%	$56.0631	$56.06	$56.05	$56.10
7 purchase totals =	$626.69		$673.8980	$673.89	$673.90	$673.90