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	$173.35	5.816%	$183.432	$183.43	$183.45	$183.40
Purchase #2	$36.76	7.147%	$39.3872	$39.39	$39.40	$39.40
Purchase #3	$154.44	5.143%	$162.3828	$162.38	$162.40	$162.40
Purchase #4	$170.72	11.842%	$190.9367	$190.94	$190.95	$190.90
Purchase #5	$123.25	11.125%	$136.9616	$136.96	$136.95	$137.00
Purchase #6	$134.34	9.702%	$147.3737	$147.37	$147.35	$147.40
Purchase #7	$171.39	11.516%	$191.1273	$191.13	$191.15	$191.10
7 purchase totals =	$964.25		$1,051.6013	$1,051.60	$1,051.65	$1,051.60