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	$89.56	12.260%	$100.5401	$100.54	$100.55	$100.50
Purchase #2	$224.58	7.154%	$240.6465	$240.65	$240.65	$240.60
Purchase #3	$227.83	12.430%	$256.1493	$256.15	$256.15	$256.10
Purchase #4	$110.33	11.727%	$123.2684	$123.27	$123.25	$123.30
Purchase #5	$22.58	12.251%	$25.3463	$25.35	$25.35	$25.30
Purchase #6	$29.33	7.104%	$31.4136	$31.41	$31.40	$31.40
Purchase #7	$110.76	7.280%	$118.8233	$118.82	$118.80	$118.80
7 purchase totals =	$814.97		$896.1875	$896.19	$896.15	$896.00