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	$242.52	12.791%	$273.5407	$273.54	$273.55	$273.50
Purchase #2	$249.25	6.697%	$265.9423	$265.94	$265.95	$265.90
Purchase #3	$130.98	5.695%	$138.4393	$138.44	$138.45	$138.40
Purchase #4	$39.47	12.108%	$44.249	$44.25	$44.25	$44.20
Purchase #5	$143.48	4.660%	$150.1662	$150.17	$150.15	$150.20
Purchase #6	$209.86	6.592%	$223.694	$223.69	$223.70	$223.70
Purchase #7	$121.27	4.304%	$126.4895	$126.49	$126.50	$126.50
7 purchase totals =	$1,136.83		$1,222.5210	$1,222.52	$1,222.55	$1,222.40