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	$28.50	11.272%	$31.7125	$31.71	$31.70	$31.70
Purchase #2	$51.51	5.851%	$54.5239	$54.52	$54.50	$54.50
Purchase #3	$231.98	10.219%	$255.686	$255.69	$255.70	$255.70
Purchase #4	$81.69	12.834%	$92.1741	$92.17	$92.15	$92.20
Purchase #5	$112.46	13.421%	$127.5533	$127.55	$127.55	$127.60
Purchase #6	$41.65	11.508%	$46.4431	$46.44	$46.45	$46.40
Purchase #7	$164.75	11.172%	$183.1559	$183.16	$183.15	$183.20
7 purchase totals =	$712.54		$791.2488	$791.24	$791.20	$791.30