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	$54.38	12.794%	$61.3374	$61.34	$61.35	$61.30
Purchase #2	$210.82	11.700%	$235.4859	$235.49	$235.50	$235.50
Purchase #3	$209.39	13.849%	$238.3884	$238.39	$238.40	$238.40
Purchase #4	$250.37	12.122%	$280.7199	$280.72	$280.70	$280.70
Purchase #5	$21.45	6.498%	$22.8438	$22.84	$22.85	$22.80
Purchase #6	$26.36	9.644%	$28.9022	$28.90	$28.90	$28.90
Purchase #7	$235.32	8.822%	$256.0799	$256.08	$256.10	$256.10
7 purchase totals =	$1,008.09		$1,123.7575	$1,123.76	$1,123.80	$1,123.70