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	$242.66	12.704%	$273.4875	$273.49	$273.50	$273.50
Purchase #2	$243.75	9.833%	$267.7179	$267.72	$267.70	$267.70
Purchase #3	$186.40	9.429%	$203.9757	$203.98	$204.00	$204.00
Purchase #4	$88.55	7.783%	$95.4418	$95.44	$95.45	$95.40
Purchase #5	$85.52	5.521%	$90.2416	$90.24	$90.25	$90.20
Purchase #6	$181.66	4.446%	$189.7366	$189.74	$189.75	$189.70
Purchase #7	$52.33	12.758%	$59.0063	$59.01	$59.00	$59.00
7 purchase totals =	$1,080.87		$1,179.6074	$1,179.62	$1,179.65	$1,179.50