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	$57.46	8.564%	$62.3809	$62.38	$62.40	$62.40
Purchase #2	$191.79	4.552%	$200.5203	$200.52	$200.50	$200.50
Purchase #3	$243.95	13.464%	$276.7954	$276.80	$276.80	$276.80
Purchase #4	$53.89	9.869%	$59.2084	$59.21	$59.20	$59.20
Purchase #5	$241.34	6.401%	$256.7882	$256.79	$256.80	$256.80
Purchase #6	$20.87	12.245%	$23.4255	$23.43	$23.45	$23.40
Purchase #7	$161.36	12.628%	$181.7365	$181.74	$181.75	$181.70
7 purchase totals =	$970.66		$1,060.8552	$1,060.87	$1,060.90	$1,060.80