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	$93.59	10.416%	$103.3383	$103.34	$103.35	$103.30
Purchase #2	$204.67	8.130%	$221.3097	$221.31	$221.30	$221.30
Purchase #3	$142.38	9.383%	$155.7395	$155.74	$155.75	$155.70
Purchase #4	$90.90	10.490%	$100.4354	$100.44	$100.45	$100.40
Purchase #5	$104.65	4.727%	$109.5968	$109.60	$109.60	$109.60
Purchase #6	$218.74	9.837%	$240.2575	$240.26	$240.25	$240.30
Purchase #7	$33.91	11.153%	$37.692	$37.69	$37.70	$37.70
7 purchase totals =	$888.84		$968.3692	$968.38	$968.40	$968.30