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	$170.91	10.112%	$188.1924	$188.19	$188.20	$188.20
Purchase #2	$201.44	7.165%	$215.8732	$215.87	$215.85	$215.90
Purchase #3	$12.52	3.400%	$12.9457	$12.95	$12.95	$12.90
Purchase #4	$183.76	7.146%	$196.8915	$196.89	$196.90	$196.90
Purchase #5	$200.82	13.262%	$227.4527	$227.45	$227.45	$227.50
Purchase #6	$135.88	7.837%	$146.5289	$146.53	$146.55	$146.50
Purchase #7	$18.34	8.185%	$19.8411	$19.84	$19.85	$19.80
7 purchase totals =	$923.67		$1,007.7255	$1,007.72	$1,007.75	$1,007.70