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	$85.88	4.264%	$89.5419	$89.54	$89.55	$89.50
Purchase #2	$235.44	11.705%	$262.9983	$263.00	$263.00	$263.00
Purchase #3	$90.56	12.437%	$101.8229	$101.82	$101.80	$101.80
Purchase #4	$232.62	12.819%	$262.4396	$262.44	$262.45	$262.40
Purchase #5	$191.95	4.611%	$200.8008	$200.80	$200.80	$200.80
Purchase #6	$43.44	13.594%	$49.3452	$49.35	$49.35	$49.30
Purchase #7	$200.61	11.515%	$223.7102	$223.71	$223.70	$223.70
7 purchase totals =	$1,080.50		$1,190.6589	$1,190.66	$1,190.65	$1,190.50