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	$32.59	12.108%	$36.536	$36.54	$36.55	$36.50
Purchase #2	$59.91	4.761%	$62.7623	$62.76	$62.75	$62.80
Purchase #3	$137.82	3.311%	$142.3832	$142.38	$142.40	$142.40
Purchase #4	$179.39	11.498%	$200.0163	$200.02	$200.00	$200.00
Purchase #5	$115.30	11.837%	$128.9481	$128.95	$128.95	$128.90
Purchase #6	$37.42	7.642%	$40.2796	$40.28	$40.30	$40.30
Purchase #7	$65.65	12.229%	$73.6783	$73.68	$73.70	$73.70
7 purchase totals =	$628.08		$684.6038	$684.61	$684.65	$684.60