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	$248.34	12.479%	$279.3303	$279.33	$279.35	$279.30
Purchase #2	$169.83	8.841%	$184.8447	$184.84	$184.85	$184.80
Purchase #3	$105.96	11.192%	$117.819	$117.82	$117.80	$117.80
Purchase #4	$181.85	7.377%	$195.2651	$195.27	$195.25	$195.30
Purchase #5	$48.29	7.343%	$51.8359	$51.84	$51.85	$51.80
Purchase #6	$70.99	3.314%	$73.3426	$73.34	$73.35	$73.30
Purchase #7	$178.30	12.638%	$200.8336	$200.83	$200.85	$200.80
7 purchase totals =	$1,003.56		$1,103.2712	$1,103.27	$1,103.30	$1,103.10