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	$94.44	5.147%	$99.3008	$99.30	$99.30	$99.30
Purchase #2	$121.82	13.661%	$138.4618	$138.46	$138.45	$138.50
Purchase #3	$190.37	12.682%	$214.5127	$214.51	$214.50	$214.50
Purchase #4	$148.85	5.378%	$156.8552	$156.86	$156.85	$156.90
Purchase #5	$150.91	13.170%	$170.7848	$170.78	$170.80	$170.80
Purchase #6	$191.79	12.681%	$216.1109	$216.11	$216.10	$216.10
Purchase #7	$173.68	4.729%	$181.8933	$181.89	$181.90	$181.90
7 purchase totals =	$1,071.86		$1,177.9195	$1,177.91	$1,177.90	$1,178.00