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	$171.75	9.687%	$188.3874	$188.39	$188.40	$188.40
Purchase #2	$133.49	6.389%	$142.0187	$142.02	$142.00	$142.00
Purchase #3	$241.91	5.783%	$255.8997	$255.90	$255.90	$255.90
Purchase #4	$200.99	11.351%	$223.8044	$223.80	$223.80	$223.80
Purchase #5	$37.80	3.142%	$38.9877	$38.99	$39.00	$39.00
Purchase #6	$93.53	5.778%	$98.9342	$98.93	$98.95	$98.90
Purchase #7	$129.46	11.175%	$143.9272	$143.93	$143.95	$143.90
7 purchase totals =	$1,008.93		$1,091.9593	$1,091.96	$1,092.00	$1,091.90