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	$172.74	5.699%	$182.5845	$182.58	$182.60	$182.60
Purchase #2	$89.96	11.594%	$100.39	$100.39	$100.40	$100.40
Purchase #3	$171.51	10.229%	$189.0538	$189.05	$189.05	$189.10
Purchase #4	$86.30	12.373%	$96.9779	$96.98	$97.00	$97.00
Purchase #5	$119.79	12.193%	$134.396	$134.40	$134.40	$134.40
Purchase #6	$32.97	5.872%	$34.906	$34.91	$34.90	$34.90
Purchase #7	$79.39	7.358%	$85.2315	$85.23	$85.25	$85.20
7 purchase totals =	$752.66		$823.5397	$823.54	$823.60	$823.60