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	$78.32	3.296%	$80.9014	$80.90	$80.90	$80.90
Purchase #2	$54.96	7.498%	$59.0809	$59.08	$59.10	$59.10
Purchase #3	$76.44	12.326%	$85.862	$85.86	$85.85	$85.90
Purchase #4	$40.57	5.769%	$42.9105	$42.91	$42.90	$42.90
Purchase #5	$100.42	10.184%	$110.6468	$110.65	$110.65	$110.60
Purchase #6	$57.51	5.448%	$60.6431	$60.64	$60.65	$60.60
Purchase #7	$72.62	7.788%	$78.2756	$78.28	$78.30	$78.30
7 purchase totals =	$480.84		$518.3203	$518.32	$518.35	$518.30