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	$235.63	4.360%	$245.9035	$245.90	$245.90	$245.90
Purchase #2	$159.92	4.463%	$167.0572	$167.06	$167.05	$167.10
Purchase #3	$132.61	7.329%	$142.329	$142.33	$142.35	$142.30
Purchase #4	$156.93	10.221%	$172.9698	$172.97	$172.95	$173.00
Purchase #5	$78.31	10.215%	$86.3094	$86.31	$86.30	$86.30
Purchase #6	$53.95	9.441%	$59.0434	$59.04	$59.05	$59.00
Purchase #7	$25.29	11.152%	$28.1103	$28.11	$28.10	$28.10
7 purchase totals =	$842.64		$901.7226	$901.72	$901.70	$901.70