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	$188.48	6.284%	$200.3241	$200.32	$200.30	$200.30
Purchase #2	$239.49	4.790%	$250.9616	$250.96	$250.95	$251.00
Purchase #3	$123.81	3.327%	$127.9292	$127.93	$127.95	$127.90
Purchase #4	$77.70	5.742%	$82.1615	$82.16	$82.15	$82.20
Purchase #5	$113.46	7.512%	$121.9831	$121.98	$122.00	$122.00
Purchase #6	$39.32	3.400%	$40.6569	$40.66	$40.65	$40.70
Purchase #7	$153.27	5.599%	$161.8516	$161.85	$161.85	$161.90
7 purchase totals =	$935.53		$985.8680	$985.86	$985.85	$986.00