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	$99.53	3.796%	$103.3082	$103.31	$103.30	$103.30
Purchase #2	$108.27	12.555%	$121.8633	$121.86	$121.85	$121.90
Purchase #3	$152.77	11.515%	$170.3615	$170.36	$170.35	$170.40
Purchase #4	$18.85	3.488%	$19.5075	$19.51	$19.50	$19.50
Purchase #5	$210.79	6.187%	$223.8316	$223.83	$223.85	$223.80
Purchase #6	$151.60	7.160%	$162.4546	$162.45	$162.45	$162.50
Purchase #7	$81.69	12.744%	$92.1006	$92.10	$92.10	$92.10
7 purchase totals =	$823.50		$893.4273	$893.42	$893.40	$893.50