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	$26.73	5.422%	$28.1793	$28.18	$28.20	$28.20
Purchase #2	$16.34	11.710%	$18.2534	$18.25	$18.25	$18.30
Purchase #3	$76.92	11.155%	$85.5004	$85.50	$85.50	$85.50
Purchase #4	$250.67	9.810%	$275.2607	$275.26	$275.25	$275.30
Purchase #5	$163.37	11.545%	$182.2311	$182.23	$182.25	$182.20
Purchase #6	$119.53	3.439%	$123.6406	$123.64	$123.65	$123.60
Purchase #7	$233.41	9.294%	$255.1031	$255.10	$255.10	$255.10
7 purchase totals =	$886.97		$968.1686	$968.16	$968.20	$968.20