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	$120.72	5.517%	$127.3801	$127.38	$127.40	$127.40
Purchase #2	$93.76	6.575%	$99.9247	$99.92	$99.90	$99.90
Purchase #3	$119.88	9.334%	$131.0696	$131.07	$131.05	$131.10
Purchase #4	$242.46	13.300%	$274.7072	$274.71	$274.70	$274.70
Purchase #5	$73.65	9.188%	$80.417	$80.42	$80.40	$80.40
Purchase #6	$114.74	7.303%	$123.1195	$123.12	$123.10	$123.10
Purchase #7	$166.60	3.670%	$172.7142	$172.71	$172.70	$172.70
7 purchase totals =	$931.81		$1,009.3323	$1,009.33	$1,009.25	$1,009.30