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	$51.50	9.366%	$56.3235	$56.32	$56.30	$56.30
Purchase #2	$44.85	11.777%	$50.132	$50.13	$50.15	$50.10
Purchase #3	$14.49	3.722%	$15.0293	$15.03	$15.05	$15.00
Purchase #4	$144.72	12.448%	$162.7347	$162.73	$162.75	$162.70
Purchase #5	$168.59	7.365%	$181.0067	$181.01	$181.00	$181.00
Purchase #6	$174.61	9.310%	$190.8662	$190.87	$190.85	$190.90
Purchase #7	$85.85	3.726%	$89.0488	$89.05	$89.05	$89.00
7 purchase totals =	$684.61		$745.1412	$745.14	$745.15	$745.00