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	$99.50	6.319%	$105.7874	$105.79	$105.80	$105.80
Purchase #2	$145.89	5.582%	$154.0336	$154.03	$154.05	$154.00
Purchase #3	$86.56	9.410%	$94.7053	$94.71	$94.70	$94.70
Purchase #4	$107.52	5.614%	$113.5562	$113.56	$113.55	$113.60
Purchase #5	$235.75	7.723%	$253.957	$253.96	$253.95	$254.00
Purchase #6	$120.55	10.615%	$133.3464	$133.35	$133.35	$133.30
Purchase #7	$213.80	11.535%	$238.4618	$238.46	$238.45	$238.50
7 purchase totals =	$1,009.57		$1,093.8477	$1,093.86	$1,093.85	$1,093.90