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	$150.26	3.222%	$155.1014	$155.10	$155.10	$155.10
Purchase #2	$88.40	13.578%	$100.403	$100.40	$100.40	$100.40
Purchase #3	$80.94	9.250%	$88.427	$88.43	$88.45	$88.40
Purchase #4	$191.81	6.630%	$204.527	$204.53	$204.55	$204.50
Purchase #5	$70.49	4.290%	$73.514	$73.51	$73.50	$73.50
Purchase #6	$126.98	5.791%	$134.3334	$134.33	$134.35	$134.30
Purchase #7	$91.84	9.279%	$100.3618	$100.36	$100.35	$100.40
7 purchase totals =	$800.72		$856.6676	$856.66	$856.70	$856.60