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	$238.90	13.141%	$270.2938	$270.29	$270.30	$270.30
Purchase #2	$78.98	8.766%	$85.9034	$85.90	$85.90	$85.90
Purchase #3	$221.63	13.523%	$251.601	$251.60	$251.60	$251.60
Purchase #4	$41.63	10.507%	$46.0041	$46.00	$46.00	$46.00
Purchase #5	$40.56	6.505%	$43.1984	$43.20	$43.20	$43.20
Purchase #6	$146.36	11.214%	$162.7728	$162.77	$162.75	$162.80
Purchase #7	$178.57	9.512%	$195.5556	$195.56	$195.55	$195.60
7 purchase totals =	$946.63		$1,055.3291	$1,055.32	$1,055.30	$1,055.40