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	$192.45	13.824%	$219.0543	$219.05	$219.05	$219.10
Purchase #2	$28.94	8.496%	$31.3987	$31.40	$31.40	$31.40
Purchase #3	$187.43	5.607%	$197.9392	$197.94	$197.95	$197.90
Purchase #4	$78.45	12.777%	$88.4736	$88.47	$88.45	$88.50
Purchase #5	$164.95	8.242%	$178.5452	$178.55	$178.55	$178.50
Purchase #6	$88.59	12.183%	$99.3829	$99.38	$99.40	$99.40
Purchase #7	$105.34	3.552%	$109.0817	$109.08	$109.10	$109.10
7 purchase totals =	$846.15		$923.8756	$923.87	$923.90	$923.90