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	$66.65	6.701%	$71.1162	$71.12	$71.10	$71.10
Purchase #2	$133.67	8.825%	$145.4664	$145.47	$145.45	$145.50
Purchase #3	$68.90	11.305%	$76.6891	$76.69	$76.70	$76.70
Purchase #4	$40.82	5.356%	$43.0063	$43.01	$43.00	$43.00
Purchase #5	$144.72	8.391%	$156.8635	$156.86	$156.85	$156.90
Purchase #6	$227.95	9.737%	$250.1455	$250.15	$250.15	$250.10
Purchase #7	$162.47	5.700%	$171.7308	$171.73	$171.75	$171.70
7 purchase totals =	$845.18		$915.0178	$915.03	$915.00	$915.00