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	$77.76	3.874%	$80.7724	$80.77	$80.75	$80.80
Purchase #2	$136.51	3.670%	$141.5199	$141.52	$141.50	$141.50
Purchase #3	$79.99	6.635%	$85.2973	$85.30	$85.30	$85.30
Purchase #4	$233.55	7.658%	$251.4353	$251.44	$251.45	$251.40
Purchase #5	$21.72	12.550%	$24.4459	$24.45	$24.45	$24.40
Purchase #6	$226.96	12.156%	$254.5493	$254.55	$254.55	$254.50
Purchase #7	$246.47	7.869%	$265.8647	$265.86	$265.85	$265.90
7 purchase totals =	$1,022.96		$1,103.8848	$1,103.89	$1,103.85	$1,103.80