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	$24.93	11.432%	$27.78	$27.78	$27.80	$27.80
Purchase #2	$165.83	8.838%	$180.4861	$180.49	$180.50	$180.50
Purchase #3	$78.89	4.652%	$82.56	$82.56	$82.55	$82.60
Purchase #4	$77.83	11.368%	$86.6777	$86.68	$86.70	$86.70
Purchase #5	$215.32	3.292%	$222.4083	$222.41	$222.40	$222.40
Purchase #6	$233.26	4.474%	$243.6961	$243.70	$243.70	$243.70
Purchase #7	$120.57	11.786%	$134.7804	$134.78	$134.80	$134.80
7 purchase totals =	$916.63		$978.3886	$978.40	$978.45	$978.50