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	$243.40	8.620%	$264.3811	$264.38	$264.40	$264.40
Purchase #2	$237.38	13.735%	$269.9841	$269.98	$270.00	$270.00
Purchase #3	$33.95	5.283%	$35.7436	$35.74	$35.75	$35.70
Purchase #4	$34.92	5.209%	$36.739	$36.74	$36.75	$36.70
Purchase #5	$111.86	13.568%	$127.0372	$127.04	$127.05	$127.00
Purchase #6	$19.44	10.767%	$21.5331	$21.53	$21.55	$21.50
Purchase #7	$211.51	5.840%	$223.8622	$223.86	$223.85	$223.90
7 purchase totals =	$892.46		$979.2803	$979.27	$979.35	$979.20