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	$74.87	6.640%	$79.8414	$79.84	$79.85	$79.80
Purchase #2	$246.61	13.801%	$280.6446	$280.64	$280.65	$280.60
Purchase #3	$168.97	6.443%	$179.8567	$179.86	$179.85	$179.90
Purchase #4	$145.41	7.651%	$156.5353	$156.54	$156.55	$156.50
Purchase #5	$5.30	10.349%	$5.8485	$5.85	$5.85	$5.80
Purchase #6	$91.85	10.574%	$101.5622	$101.56	$101.55	$101.60
Purchase #7	$72.39	11.330%	$80.5918	$80.59	$80.60	$80.60
7 purchase totals =	$805.40		$884.8805	$884.88	$884.90	$884.80