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	$101.30	5.149%	$106.5159	$106.52	$106.50	$106.50
Purchase #2	$78.82	3.354%	$81.4636	$81.46	$81.45	$81.50
Purchase #3	$110.83	12.571%	$124.7624	$124.76	$124.75	$124.80
Purchase #4	$41.47	10.873%	$45.979	$45.98	$46.00	$46.00
Purchase #5	$144.86	5.399%	$152.681	$152.68	$152.70	$152.70
Purchase #6	$78.57	8.346%	$85.1275	$85.13	$85.15	$85.10
Purchase #7	$64.41	11.215%	$71.6336	$71.63	$71.65	$71.60
7 purchase totals =	$620.26		$668.1630	$668.16	$668.20	$668.20