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	$55.48	3.437%	$57.3868	$57.39	$57.40	$57.40
Purchase #2	$228.82	9.600%	$250.7867	$250.79	$250.80	$250.80
Purchase #3	$93.84	6.363%	$99.811	$99.81	$99.80	$99.80
Purchase #4	$39.41	13.636%	$44.7839	$44.78	$44.80	$44.80
Purchase #5	$153.50	3.116%	$158.2831	$158.28	$158.30	$158.30
Purchase #6	$177.38	5.393%	$186.9461	$186.95	$186.95	$186.90
Purchase #7	$42.70	9.769%	$46.8714	$46.87	$46.85	$46.90
7 purchase totals =	$791.13		$844.8690	$844.87	$844.90	$844.90