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	$137.98	6.241%	$146.5913	$146.59	$146.60	$146.60
Purchase #2	$92.92	12.294%	$104.3436	$104.34	$104.35	$104.30
Purchase #3	$82.43	7.115%	$88.2949	$88.29	$88.30	$88.30
Purchase #4	$94.37	9.704%	$103.5277	$103.53	$103.55	$103.50
Purchase #5	$85.42	4.808%	$89.527	$89.53	$89.55	$89.50
Purchase #6	$247.86	12.316%	$278.3864	$278.39	$278.40	$278.40
Purchase #7	$208.81	6.340%	$222.0486	$222.05	$222.05	$222.00
7 purchase totals =	$949.79		$1,032.7195	$1,032.72	$1,032.80	$1,032.60