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	$110.33	11.754%	$123.2982	$123.30	$123.30	$123.30
Purchase #2	$45.74	12.782%	$51.5865	$51.59	$51.60	$51.60
Purchase #3	$151.80	10.782%	$168.1671	$168.17	$168.15	$168.20
Purchase #4	$201.84	10.856%	$223.7518	$223.75	$223.75	$223.80
Purchase #5	$213.51	11.569%	$238.211	$238.21	$238.20	$238.20
Purchase #6	$42.99	5.238%	$45.2418	$45.24	$45.25	$45.20
Purchase #7	$243.39	5.418%	$256.5769	$256.58	$256.60	$256.60
7 purchase totals =	$1,009.60		$1,106.8333	$1,106.84	$1,106.85	$1,106.90