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	$170.53	9.196%	$186.2119	$186.21	$186.20	$186.20
Purchase #2	$75.87	9.161%	$82.8205	$82.82	$82.80	$82.80
Purchase #3	$83.84	6.726%	$89.4791	$89.48	$89.50	$89.50
Purchase #4	$68.81	11.718%	$76.8732	$76.87	$76.85	$76.90
Purchase #5	$85.45	4.410%	$89.2183	$89.22	$89.20	$89.20
Purchase #6	$45.32	7.653%	$48.7883	$48.79	$48.80	$48.80
Purchase #7	$142.75	6.354%	$151.8203	$151.82	$151.80	$151.80
7 purchase totals =	$672.57		$725.2116	$725.21	$725.15	$725.20