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	$245.77	6.158%	$260.9045	$260.90	$260.90	$260.90
Purchase #2	$16.54	13.814%	$18.8248	$18.82	$18.80	$18.80
Purchase #3	$114.88	7.460%	$123.45	$123.45	$123.45	$123.50
Purchase #4	$242.93	4.552%	$253.9882	$253.99	$254.00	$254.00
Purchase #5	$84.56	13.368%	$95.864	$95.86	$95.85	$95.90
Purchase #6	$140.30	6.376%	$149.2455	$149.25	$149.25	$149.20
Purchase #7	$30.47	9.111%	$33.2461	$33.25	$33.25	$33.20
7 purchase totals =	$875.45		$935.5231	$935.52	$935.50	$935.50