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	$120.60	11.512%	$134.4835	$134.48	$134.50	$134.50
Purchase #2	$214.36	8.145%	$231.8196	$231.82	$231.80	$231.80
Purchase #3	$85.80	12.639%	$96.6443	$96.64	$96.65	$96.60
Purchase #4	$90.34	13.486%	$102.5233	$102.52	$102.50	$102.50
Purchase #5	$59.26	11.235%	$65.9179	$65.92	$65.90	$65.90
Purchase #6	$186.52	12.768%	$210.3349	$210.33	$210.35	$210.30
Purchase #7	$149.58	8.672%	$162.5516	$162.55	$162.55	$162.60
7 purchase totals =	$906.46		$1,004.2751	$1,004.26	$1,004.25	$1,004.20