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	$9.40	3.332%	$9.7132	$9.71	$9.70	$9.70
Purchase #2	$40.41	8.665%	$43.9115	$43.91	$43.90	$43.90
Purchase #3	$86.72	3.571%	$89.8168	$89.82	$89.80	$89.80
Purchase #4	$101.41	13.127%	$114.7221	$114.72	$114.70	$114.70
Purchase #5	$232.64	4.593%	$243.3252	$243.33	$243.35	$243.30
Purchase #6	$229.33	11.199%	$255.0127	$255.01	$255.00	$255.00
Purchase #7	$202.81	10.272%	$223.6426	$223.64	$223.65	$223.60
7 purchase totals =	$902.72		$980.1441	$980.14	$980.10	$980.00