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	$75.79	9.380%	$82.8991	$82.90	$82.90	$82.90
Purchase #2	$235.56	4.209%	$245.4747	$245.47	$245.45	$245.50
Purchase #3	$202.42	10.326%	$223.3219	$223.32	$223.30	$223.30
Purchase #4	$64.58	13.804%	$73.4946	$73.49	$73.50	$73.50
Purchase #5	$93.88	6.500%	$99.9822	$99.98	$100.00	$100.00
Purchase #6	$69.31	8.858%	$75.4495	$75.45	$75.45	$75.40
Purchase #7	$163.27	10.761%	$180.8395	$180.84	$180.85	$180.80
7 purchase totals =	$904.81		$981.4615	$981.45	$981.45	$981.40