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	$25.33	5.208%	$26.6492	$26.65	$26.65	$26.60
Purchase #2	$52.60	12.260%	$59.0488	$59.05	$59.05	$59.00
Purchase #3	$96.45	13.568%	$109.5363	$109.54	$109.55	$109.50
Purchase #4	$99.26	4.321%	$103.549	$103.55	$103.55	$103.50
Purchase #5	$40.62	8.118%	$43.9175	$43.92	$43.90	$43.90
Purchase #6	$247.40	5.732%	$261.581	$261.58	$261.60	$261.60
Purchase #7	$36.65	4.223%	$38.1977	$38.20	$38.20	$38.20
7 purchase totals =	$598.31		$642.4795	$642.49	$642.50	$642.30