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	$149.95	11.758%	$167.5811	$167.58	$167.60	$167.60
Purchase #2	$133.39	4.642%	$139.582	$139.58	$139.60	$139.60
Purchase #3	$25.56	11.517%	$28.5037	$28.50	$28.50	$28.50
Purchase #4	$141.33	8.672%	$153.5861	$153.59	$153.60	$153.60
Purchase #5	$90.54	12.592%	$101.9408	$101.94	$101.95	$101.90
Purchase #6	$172.40	11.232%	$191.764	$191.76	$191.75	$191.80
Purchase #7	$160.77	4.449%	$167.9227	$167.92	$167.90	$167.90
7 purchase totals =	$873.94		$950.8804	$950.87	$950.90	$950.90