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	$26.94	3.751%	$27.9505	$27.95	$27.95	$28.00
Purchase #2	$59.38	4.804%	$62.2326	$62.23	$62.25	$62.20
Purchase #3	$30.90	6.800%	$33.0012	$33.00	$33.00	$33.00
Purchase #4	$89.61	12.117%	$100.468	$100.47	$100.45	$100.50
Purchase #5	$59.75	12.804%	$67.4004	$67.40	$67.40	$67.40
Purchase #6	$25.32	10.565%	$27.9951	$28.00	$28.00	$28.00
Purchase #7	$174.79	10.466%	$193.0835	$193.08	$193.10	$193.10
7 purchase totals =	$466.69		$512.1313	$512.13	$512.15	$512.20