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	$32.66	10.759%	$36.1739	$36.17	$36.15	$36.20
Purchase #2	$133.86	11.228%	$148.8898	$148.89	$148.90	$148.90
Purchase #3	$83.87	6.693%	$89.4834	$89.48	$89.50	$89.50
Purchase #4	$191.84	12.791%	$216.3783	$216.38	$216.40	$216.40
Purchase #5	$190.42	10.393%	$210.2104	$210.21	$210.20	$210.20
Purchase #6	$51.81	4.350%	$54.0637	$54.06	$54.05	$54.10
Purchase #7	$225.90	10.720%	$250.1165	$250.12	$250.10	$250.10
7 purchase totals =	$910.36		$1,005.3160	$1,005.31	$1,005.30	$1,005.40