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	$27.36	12.762%	$30.8517	$30.85	$30.85	$30.90
Purchase #2	$53.42	12.130%	$59.8998	$59.90	$59.90	$59.90
Purchase #3	$149.67	4.714%	$156.7254	$156.73	$156.75	$156.70
Purchase #4	$249.27	13.526%	$282.9863	$282.99	$283.00	$283.00
Purchase #5	$82.61	11.483%	$92.0961	$92.10	$92.10	$92.10
Purchase #6	$87.46	10.213%	$96.3923	$96.39	$96.40	$96.40
Purchase #7	$62.32	5.271%	$65.6049	$65.60	$65.60	$65.60
7 purchase totals =	$712.11		$784.5565	$784.56	$784.60	$784.60