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	$51.68	6.429%	$55.0025	$55.00	$55.00	$55.00
Purchase #2	$148.27	13.654%	$168.5148	$168.51	$168.50	$168.50
Purchase #3	$199.87	9.774%	$219.4053	$219.41	$219.40	$219.40
Purchase #4	$221.91	12.728%	$250.1547	$250.15	$250.15	$250.20
Purchase #5	$202.40	13.354%	$229.4285	$229.43	$229.45	$229.40
Purchase #6	$86.70	7.710%	$93.3846	$93.38	$93.40	$93.40
Purchase #7	$152.68	7.807%	$164.5997	$164.60	$164.60	$164.60
7 purchase totals =	$1,063.51		$1,180.4901	$1,180.48	$1,180.50	$1,180.50