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	$124.51	12.559%	$140.1472	$140.15	$140.15	$140.10
Purchase #2	$59.62	8.130%	$64.4671	$64.47	$64.45	$64.50
Purchase #3	$15.36	3.474%	$15.8936	$15.89	$15.90	$15.90
Purchase #4	$39.50	6.873%	$42.2148	$42.21	$42.20	$42.20
Purchase #5	$219.39	5.539%	$231.542	$231.54	$231.55	$231.50
Purchase #6	$7.45	11.654%	$8.3182	$8.32	$8.30	$8.30
Purchase #7	$103.64	10.347%	$114.3636	$114.36	$114.35	$114.40
7 purchase totals =	$569.47		$616.9465	$616.94	$616.90	$616.90