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	$99.39	10.213%	$109.5407	$109.54	$109.55	$109.50
Purchase #2	$170.38	10.611%	$188.459	$188.46	$188.45	$188.50
Purchase #3	$147.43	5.805%	$155.9883	$155.99	$156.00	$156.00
Purchase #4	$178.43	10.528%	$197.2151	$197.22	$197.20	$197.20
Purchase #5	$166.92	13.592%	$189.6078	$189.61	$189.60	$189.60
Purchase #6	$56.82	10.640%	$62.8656	$62.87	$62.85	$62.90
Purchase #7	$147.48	10.372%	$162.7766	$162.78	$162.80	$162.80
7 purchase totals =	$966.85		$1,066.4531	$1,066.47	$1,066.45	$1,066.50