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	$198.89	4.571%	$207.9813	$207.98	$208.00	$208.00
Purchase #2	$174.73	6.228%	$185.6122	$185.61	$185.60	$185.60
Purchase #3	$80.67	5.327%	$84.9673	$84.97	$84.95	$85.00
Purchase #4	$7.39	11.610%	$8.248	$8.25	$8.25	$8.20
Purchase #5	$30.77	9.243%	$33.6141	$33.61	$33.60	$33.60
Purchase #6	$58.40	7.181%	$62.5937	$62.59	$62.60	$62.60
Purchase #7	$80.88	3.234%	$83.4957	$83.50	$83.50	$83.50
7 purchase totals =	$631.73		$666.5123	$666.51	$666.50	$666.50