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	$47.85	11.404%	$53.3068	$53.31	$53.30	$53.30
Purchase #2	$27.62	6.630%	$29.4512	$29.45	$29.45	$29.50
Purchase #3	$116.55	5.134%	$122.5337	$122.53	$122.55	$122.50
Purchase #4	$9.77	6.331%	$10.3885	$10.39	$10.40	$10.40
Purchase #5	$126.91	11.400%	$141.3777	$141.38	$141.40	$141.40
Purchase #6	$207.54	10.293%	$228.9021	$228.90	$228.90	$228.90
Purchase #7	$73.64	9.172%	$80.3943	$80.39	$80.40	$80.40
7 purchase totals =	$609.88		$666.3543	$666.35	$666.40	$666.40