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	$245.25	3.501%	$253.8362	$253.84	$253.85	$253.80
Purchase #2	$245.42	10.172%	$270.3841	$270.38	$270.40	$270.40
Purchase #3	$147.37	5.499%	$155.4739	$155.47	$155.45	$155.50
Purchase #4	$148.34	9.243%	$162.0511	$162.05	$162.05	$162.10
Purchase #5	$66.49	9.564%	$72.8491	$72.85	$72.85	$72.80
Purchase #6	$39.79	12.705%	$44.8453	$44.85	$44.85	$44.80
Purchase #7	$119.58	11.277%	$133.065	$133.07	$133.05	$133.10
7 purchase totals =	$1,012.24		$1,092.5047	$1,092.51	$1,092.50	$1,092.50