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	$78.83	6.200%	$83.7175	$83.72	$83.70	$83.70
Purchase #2	$75.42	7.674%	$81.2077	$81.21	$81.20	$81.20
Purchase #3	$172.45	5.761%	$182.3848	$182.38	$182.40	$182.40
Purchase #4	$134.43	5.368%	$141.6462	$141.65	$141.65	$141.60
Purchase #5	$70.27	10.641%	$77.7474	$77.75	$77.75	$77.70
Purchase #6	$128.65	10.737%	$142.4632	$142.46	$142.45	$142.50
Purchase #7	$109.80	6.360%	$116.7833	$116.78	$116.80	$116.80
7 purchase totals =	$769.85		$825.9501	$825.95	$825.95	$825.90