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	$170.83	3.324%	$176.5084	$176.51	$176.50	$176.50
Purchase #2	$250.47	6.688%	$267.2214	$267.22	$267.20	$267.20
Purchase #3	$162.70	13.783%	$185.1249	$185.12	$185.10	$185.10
Purchase #4	$28.34	13.774%	$32.2436	$32.24	$32.25	$32.20
Purchase #5	$188.91	6.328%	$200.8642	$200.86	$200.85	$200.90
Purchase #6	$19.41	3.105%	$20.0127	$20.01	$20.00	$20.00
Purchase #7	$211.72	4.546%	$221.3448	$221.34	$221.35	$221.30
7 purchase totals =	$1,032.38		$1,103.3200	$1,103.30	$1,103.25	$1,103.20