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	$75.72	12.609%	$85.2675	$85.27	$85.25	$85.30
Purchase #2	$65.48	9.130%	$71.4583	$71.46	$71.45	$71.50
Purchase #3	$41.52	11.229%	$46.1823	$46.18	$46.20	$46.20
Purchase #4	$118.61	13.646%	$134.7955	$134.80	$134.80	$134.80
Purchase #5	$28.44	10.141%	$31.3241	$31.32	$31.30	$31.30
Purchase #6	$249.52	12.315%	$280.2484	$280.25	$280.25	$280.20
Purchase #7	$231.53	4.855%	$242.7708	$242.77	$242.75	$242.80
7 purchase totals =	$810.82		$892.0469	$892.05	$892.00	$892.10