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	$13.85	12.392%	$15.5663	$15.57	$15.55	$15.60
Purchase #2	$250.39	12.130%	$280.7623	$280.76	$280.75	$280.80
Purchase #3	$225.79	12.331%	$253.6322	$253.63	$253.65	$253.60
Purchase #4	$39.26	10.491%	$43.3788	$43.38	$43.40	$43.40
Purchase #5	$140.43	11.614%	$156.7395	$156.74	$156.75	$156.70
Purchase #6	$155.73	7.456%	$167.3412	$167.34	$167.35	$167.30
Purchase #7	$250.41	12.618%	$282.0067	$282.01	$282.00	$282.00
7 purchase totals =	$1,075.86		$1,199.4270	$1,199.43	$1,199.45	$1,199.40