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	$199.42	11.234%	$221.8228	$221.82	$221.80	$221.80
Purchase #2	$245.87	6.778%	$262.5351	$262.54	$262.55	$262.50
Purchase #3	$144.69	9.862%	$158.9593	$158.96	$158.95	$159.00
Purchase #4	$195.59	10.134%	$215.4111	$215.41	$215.40	$215.40
Purchase #5	$123.31	6.150%	$130.8936	$130.89	$130.90	$130.90
Purchase #6	$232.54	7.617%	$250.2526	$250.25	$250.25	$250.30
Purchase #7	$49.75	8.863%	$54.1593	$54.16	$54.15	$54.20
7 purchase totals =	$1,191.17		$1,294.0338	$1,294.03	$1,294.00	$1,294.10