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	$230.25	3.646%	$238.6449	$238.64	$238.65	$238.60
Purchase #2	$127.97	11.355%	$142.501	$142.50	$142.50	$142.50
Purchase #3	$121.75	4.424%	$127.1362	$127.14	$127.15	$127.10
Purchase #4	$29.29	9.690%	$32.1282	$32.13	$32.15	$32.10
Purchase #5	$58.59	6.166%	$62.2027	$62.20	$62.20	$62.20
Purchase #6	$243.26	9.296%	$265.8734	$265.87	$265.85	$265.90
Purchase #7	$167.73	12.791%	$189.1843	$189.18	$189.20	$189.20
7 purchase totals =	$978.84		$1,057.6707	$1,057.66	$1,057.70	$1,057.60