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	$163.33	10.523%	$180.5172	$180.52	$180.50	$180.50
Purchase #2	$81.46	9.322%	$89.0537	$89.05	$89.05	$89.10
Purchase #3	$249.90	9.332%	$273.2207	$273.22	$273.20	$273.20
Purchase #4	$210.31	6.160%	$223.2651	$223.27	$223.25	$223.30
Purchase #5	$147.30	6.638%	$157.0778	$157.08	$157.10	$157.10
Purchase #6	$214.45	11.211%	$238.492	$238.49	$238.50	$238.50
Purchase #7	$93.53	7.125%	$100.194	$100.19	$100.20	$100.20
7 purchase totals =	$1,160.28		$1,261.8205	$1,261.82	$1,261.80	$1,261.90