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	$19.95	3.804%	$20.7089	$20.71	$20.70	$20.70
Purchase #2	$128.39	12.544%	$144.4952	$144.50	$144.50	$144.50
Purchase #3	$211.76	10.446%	$233.8804	$233.88	$233.90	$233.90
Purchase #4	$118.30	4.712%	$123.8743	$123.87	$123.85	$123.90
Purchase #5	$244.86	3.512%	$253.4595	$253.46	$253.45	$253.50
Purchase #6	$88.29	11.256%	$98.2279	$98.23	$98.25	$98.20
Purchase #7	$73.53	4.597%	$76.9102	$76.91	$76.90	$76.90
7 purchase totals =	$885.08		$951.5564	$951.56	$951.55	$951.60