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	$238.28	5.118%	$250.4752	$250.48	$250.50	$250.50
Purchase #2	$39.63	9.588%	$43.4297	$43.43	$43.45	$43.40
Purchase #3	$226.77	13.248%	$256.8125	$256.81	$256.80	$256.80
Purchase #4	$165.91	6.199%	$176.1948	$176.19	$176.20	$176.20
Purchase #5	$164.40	6.766%	$175.5233	$175.52	$175.50	$175.50
Purchase #6	$192.42	11.183%	$213.9383	$213.94	$213.95	$213.90
Purchase #7	$28.69	9.168%	$31.3203	$31.32	$31.30	$31.30
7 purchase totals =	$1,056.10		$1,147.6941	$1,147.69	$1,147.70	$1,147.60