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	$75.34	6.528%	$80.2582	$80.26	$80.25	$80.30
Purchase #2	$65.99	7.681%	$71.0587	$71.06	$71.05	$71.10
Purchase #3	$241.34	12.603%	$271.7561	$271.76	$271.75	$271.80
Purchase #4	$30.28	3.867%	$31.4509	$31.45	$31.45	$31.50
Purchase #5	$32.43	6.131%	$34.4183	$34.42	$34.40	$34.40
Purchase #6	$246.90	3.234%	$254.8847	$254.88	$254.90	$254.90
Purchase #7	$243.73	12.360%	$273.855	$273.86	$273.85	$273.90
7 purchase totals =	$936.01		$1,017.6819	$1,017.69	$1,017.65	$1,017.90