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	$130.38	4.779%	$136.6109	$136.61	$136.60	$136.60
Purchase #2	$121.59	7.775%	$131.0436	$131.04	$131.05	$131.00
Purchase #3	$5.79	4.822%	$6.0692	$6.07	$6.05	$6.10
Purchase #4	$48.67	5.484%	$51.3391	$51.34	$51.35	$51.30
Purchase #5	$97.56	4.318%	$101.7726	$101.77	$101.75	$101.80
Purchase #6	$74.64	10.478%	$82.4608	$82.46	$82.45	$82.50
Purchase #7	$124.94	13.124%	$141.3371	$141.34	$141.35	$141.30
7 purchase totals =	$603.57		$650.6333	$650.63	$650.60	$650.60