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	$126.63	11.662%	$141.3976	$141.40	$141.40	$141.40
Purchase #2	$181.55	10.428%	$200.482	$200.48	$200.50	$200.50
Purchase #3	$149.52	10.737%	$165.574	$165.57	$165.55	$165.60
Purchase #4	$152.81	12.618%	$172.0916	$172.09	$172.10	$172.10
Purchase #5	$198.46	12.440%	$223.1484	$223.15	$223.15	$223.10
Purchase #6	$19.91	8.229%	$21.5484	$21.55	$21.55	$21.50
Purchase #7	$46.96	12.706%	$52.9267	$52.93	$52.95	$52.90
7 purchase totals =	$875.84		$977.1687	$977.17	$977.20	$977.10