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	$234.33	11.382%	$261.0014	$261.00	$261.00	$261.00
Purchase #2	$238.74	4.846%	$250.3093	$250.31	$250.30	$250.30
Purchase #3	$139.43	11.247%	$155.1117	$155.11	$155.10	$155.10
Purchase #4	$180.45	5.787%	$190.8926	$190.89	$190.90	$190.90
Purchase #5	$27.48	5.166%	$28.8996	$28.90	$28.90	$28.90
Purchase #6	$137.60	10.395%	$151.9035	$151.90	$151.90	$151.90
Purchase #7	$203.29	6.233%	$215.9611	$215.96	$215.95	$216.00
7 purchase totals =	$1,161.32		$1,254.0792	$1,254.07	$1,254.05	$1,254.10