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	$166.76	12.193%	$187.093	$187.09	$187.10	$187.10
Purchase #2	$202.64	4.283%	$211.3191	$211.32	$211.30	$211.30
Purchase #3	$73.61	11.839%	$82.3247	$82.32	$82.30	$82.30
Purchase #4	$134.38	6.810%	$143.5313	$143.53	$143.55	$143.50
Purchase #5	$36.40	12.573%	$40.9766	$40.98	$41.00	$41.00
Purchase #6	$127.72	11.579%	$142.5087	$142.51	$142.50	$142.50
Purchase #7	$167.48	11.298%	$186.4019	$186.40	$186.40	$186.40
7 purchase totals =	$908.99		$994.1553	$994.15	$994.15	$994.10