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	$84.96	6.786%	$90.7254	$90.73	$90.75	$90.70
Purchase #2	$167.52	7.636%	$180.3118	$180.31	$180.30	$180.30
Purchase #3	$72.76	9.784%	$79.8788	$79.88	$79.90	$79.90
Purchase #4	$74.44	5.737%	$78.7106	$78.71	$78.70	$78.70
Purchase #5	$145.45	6.540%	$154.9624	$154.96	$154.95	$155.00
Purchase #6	$36.55	11.197%	$40.6425	$40.64	$40.65	$40.60
Purchase #7	$26.69	4.208%	$27.8131	$27.81	$27.80	$27.80
7 purchase totals =	$608.37		$653.0446	$653.04	$653.05	$653.00