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	$170.63	12.398%	$191.7847	$191.78	$191.80	$191.80
Purchase #2	$78.94	4.546%	$82.5286	$82.53	$82.55	$82.50
Purchase #3	$180.80	13.150%	$204.5752	$204.58	$204.60	$204.60
Purchase #4	$217.53	13.142%	$246.1178	$246.12	$246.10	$246.10
Purchase #5	$80.52	9.715%	$88.3425	$88.34	$88.35	$88.30
Purchase #6	$136.54	6.454%	$145.3523	$145.35	$145.35	$145.40
Purchase #7	$124.64	4.731%	$130.5367	$130.54	$130.55	$130.50
7 purchase totals =	$989.60		$1,089.2378	$1,089.24	$1,089.30	$1,089.20