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	$74.28	11.643%	$82.9284	$82.93	$82.95	$82.90
Purchase #2	$118.90	8.437%	$128.9316	$128.93	$128.95	$128.90
Purchase #3	$28.38	7.587%	$30.5332	$30.53	$30.55	$30.50
Purchase #4	$97.54	13.484%	$110.6923	$110.69	$110.70	$110.70
Purchase #5	$151.61	4.439%	$158.34	$158.34	$158.35	$158.30
Purchase #6	$56.76	5.447%	$59.8517	$59.85	$59.85	$59.90
Purchase #7	$77.37	3.318%	$79.9371	$79.94	$79.95	$79.90
7 purchase totals =	$604.84		$651.2143	$651.21	$651.30	$651.10