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	$128.60	8.540%	$139.5824	$139.58	$139.60	$139.60
Purchase #2	$47.65	12.593%	$53.6506	$53.65	$53.65	$53.70
Purchase #3	$223.61	11.484%	$249.2894	$249.29	$249.30	$249.30
Purchase #4	$243.77	10.258%	$268.7759	$268.78	$268.80	$268.80
Purchase #5	$37.93	12.266%	$42.5825	$42.58	$42.60	$42.60
Purchase #6	$146.77	10.462%	$162.1251	$162.13	$162.15	$162.10
Purchase #7	$135.36	7.479%	$145.4836	$145.48	$145.50	$145.50
7 purchase totals =	$963.69		$1,061.4895	$1,061.49	$1,061.60	$1,061.60