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	$41.29	3.874%	$42.8896	$42.89	$42.90	$42.90
Purchase #2	$153.39	13.814%	$174.5793	$174.58	$174.60	$174.60
Purchase #3	$142.38	11.424%	$158.6455	$158.65	$158.65	$158.60
Purchase #4	$106.92	9.606%	$117.1907	$117.19	$117.20	$117.20
Purchase #5	$42.25	12.280%	$47.4383	$47.44	$47.45	$47.40
Purchase #6	$95.39	4.797%	$99.9659	$99.97	$99.95	$100.00
Purchase #7	$170.64	8.506%	$185.1546	$185.15	$185.15	$185.20
7 purchase totals =	$752.26		$825.8639	$825.87	$825.90	$825.90