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	$63.77	11.609%	$71.1731	$71.17	$71.15	$71.20
Purchase #2	$193.39	8.599%	$210.0196	$210.02	$210.00	$210.00
Purchase #3	$165.97	7.117%	$177.7821	$177.78	$177.80	$177.80
Purchase #4	$60.39	11.419%	$67.2859	$67.29	$67.30	$67.30
Purchase #5	$37.43	10.300%	$41.2853	$41.29	$41.30	$41.30
Purchase #6	$249.89	6.760%	$266.7826	$266.78	$266.80	$266.80
Purchase #7	$121.89	4.617%	$127.5177	$127.52	$127.50	$127.50
7 purchase totals =	$892.73		$961.8463	$961.85	$961.85	$961.90