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	$26.30	5.520%	$27.7518	$27.75	$27.75	$27.80
Purchase #2	$47.37	13.661%	$53.8412	$53.84	$53.85	$53.80
Purchase #3	$139.76	4.298%	$145.7669	$145.77	$145.75	$145.80
Purchase #4	$154.48	3.830%	$160.3966	$160.40	$160.40	$160.40
Purchase #5	$234.33	5.425%	$247.0424	$247.04	$247.05	$247.00
Purchase #6	$246.46	13.834%	$280.5553	$280.56	$280.55	$280.60
Purchase #7	$55.57	10.874%	$61.6127	$61.61	$61.60	$61.60
7 purchase totals =	$904.27		$976.9669	$976.97	$976.95	$977.00