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	$90.49	4.675%	$94.7204	$94.72	$94.70	$94.70
Purchase #2	$213.78	7.202%	$229.1764	$229.18	$229.20	$229.20
Purchase #3	$48.56	13.709%	$55.2171	$55.22	$55.20	$55.20
Purchase #4	$116.98	12.535%	$131.6434	$131.64	$131.65	$131.60
Purchase #5	$119.68	6.398%	$127.3371	$127.34	$127.35	$127.30
Purchase #6	$196.42	10.403%	$216.8536	$216.85	$216.85	$216.90
Purchase #7	$25.42	10.347%	$28.0502	$28.05	$28.05	$28.10
7 purchase totals =	$811.33		$882.9982	$883.00	$883.00	$883.00