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	$136.52	11.260%	$151.8922	$151.89	$151.90	$151.90
Purchase #2	$111.57	11.146%	$124.0056	$124.01	$124.00	$124.00
Purchase #3	$185.48	10.781%	$205.4766	$205.48	$205.50	$205.50
Purchase #4	$134.79	3.324%	$139.2704	$139.27	$139.25	$139.30
Purchase #5	$182.43	11.225%	$202.9078	$202.91	$202.90	$202.90
Purchase #6	$78.93	3.266%	$81.5079	$81.51	$81.50	$81.50
Purchase #7	$29.83	10.818%	$33.057	$33.06	$33.05	$33.10
7 purchase totals =	$859.55		$938.1175	$938.13	$938.10	$938.20